Commentary on Aquinas’s Five Ways by Fr. Brian Davies O.P.

Chapter 3:

Knowing That God Exists (1a,1,2)

Summa Theologiae 1a,2 is titled de Deo, an Deus sit (“Does God exist?”). Consisting of only three much-quoted articles, it gives us the start of the Sum ma’s treatment of natural theology.¹ Aquinas believes that before embarking on a “scientific” study of anything we need to know that the thing in question exists, and this is the thought that governs what he says in 1a,2. Aquinas distinguishes between the questions an est (“Does it exist?”) and quid est (“What is it?”), and he will turn to the question “What is God?” in 1a,3. In 1a,2, however, his focus is on what we might call “the mere existence” of God. Does this mean that 1a,2 is offered by Aquinas as a help to people with no belief in God? Not quite, given 1a,1. Even in 1a,2, Aquinas is writing for Christians. Yet Aquinas does think that a good philosophical case can be made in defense of the truth of the proposition “God exists,” and in 1a,2 he aims to indicate what that case amounts to.

3.1 Per se Notum (1a,2,1)

Aquinas’s position is that we can only know that God exists by means of causal inference from God’s effects.² He is, however, aware that some people have taken “God exists” (Deus est) to be known to be true without reference to causal reasoning. He discusses this way of thinking in 1a,2,1, where he raises the question “Is it self-evident (per se notum) that God exists?”

Per se notum literally means “known through itself,” and Aquinas takes the claim that “God exists” is per se notum to hold that the truth of “God exists” is something we can arrive at by virtue of some understanding we have of God not grounded in causal reasoning—that “God exists” is known by us in some basic way just because we are thinking things that we are.³ More specifically, in 1a,2,1 he takes it to amount to three arguments: (1) Knowledge of God is implanted in us by nature; (2) Once we understand what the word “God” means, we can see that it would be self-contradictory to deny that God exists; (3) Since God is Truth, and since we cannot consistently assert that it is true that there is no truth, God evidently exists. Aquinas is partly sympathetic to these arguments. He agrees, for example, that everyone has a desire for God since everyone naturally desires happiness and since our ultimate happiness is to be found only in God. He also agrees that if we could understand what God is we would immediately see that God cannot but exist. And he accepts that there evidently is such a thing as truth. At the same time, however, he rejects (1) to (3) just noted. Vaguely to desire God is not, he says, to know that God exists any more than to recognize that someone is coming is to know who exactly it is that is coming. And there being truth in general does not imply that there is anything to be dignified by the title “First Truth” (i.e., God).

Argument (2) is today, perhaps, the best known version of what Aquinas has in mind when thinking of the claim that Deus est is per se notum. That is because, as Aquinas presents it in 1a,2,1, it reads like a famous argument (usually referred to as the “Ontological Argument”) first presented by St. Anselm of Canterbury (1033–1109) in his Proslogion.⁴ This argument is de fended by some philosophers today, so there is a lot of contemporary literature on it.⁵ As Aquinas presents the argument (without citing Anselm as its source), it runs: “Once we understand the meaning of the word ‘God,’ we immediately see that God exists. For the word means ‘that than which nothing greater can be signified.’ So, since what exists in thought and fact is greater than what exists in thought alone, and since, once we understand the word ‘God,’ God exists in thought, God must also exist in fact.”⁶

Anselm says more than this in defense of his ontological argument, but Aquinas seems unconcerned with the details of Anselm’s argument or with Anselm’s defense of himself to one of his contemporaries.⁷ Rather, he focuses on the general idea that we have an understanding of God that leaves us being inconsistent should we go on to deny that God exists. He writes:

Even if someone thinks that what is signified by ‘God’ is ‘that than which nothing greater can be thought’, it does not follow that the person in question thinks that what is signified by ‘God’ exists in reality rather than merely as thought about. If we do not grant that something in fact exists than which nothing greater can be thought (and nobody denying the existence of God would grant this), the conclusion that God in fact exists does not follow.

Critics of versions of the Ontological Argument have often suggested that we cannot conclude from the meaning of the word “God” that there is anything in reality corresponding to it, and Aquinas seems to support this line of thinking, though he does agree that a knowledge of what God actually is would leave us with an understanding that God has to be. In 1a,3, he will argue that it is God’s nature to exist. So Aquinas does think that God cannot but exist. In 1a,2,1, however, he is criticizing approaches defending the truth of Deus est, which seem to presume a knowledge concerning God that, in Aquinas’s view, we lack. He makes a distinction between what is per se notum in itself (per se) and what is per se notum to us (quoad nos). He thinks that Deus est is “self evident in itself” in that it is God’s nature to exist. But, as we shall soon see, he denies that we have a God’s-eye view of what God is.

3.2 Demonstrating That God Exists (1a,2,2–3)

Some philosophers have said that we come to know that God exists by employing what they call “intuition.” The idea here is that, with no reliance on inferential argument, we know that God exists by just seeing all at once that this is so.⁸ Such is not Aquinas’s view, however, and in 1a,2,2 and 3 he maintains that we can demonstrate that God exists. Yet what does Aquinas mean by “demonstrate” and “demonstration”? He takes a demonstration to be an argument that, starting with true premises, entails its conclusion formally or validly. Here Aquinas is drawing on Aristotle’s Posterior Analytics.

He takes a demonstrative argument to have the form: (1) “All X is Y” (e.g., “All human beings are mammals”); (2) “All Y is Z” (e.g., “All mammals breathe air”); (3) “Therefore, All X is Z” (e.g., “Therefore, all human beings breathe air”). Given (1) and (2), (3) follows necessarily. This is not to say, as some would, that (1) to (3) erroneously “beg the question” since (3) seems to be somehow “contained” in (1) and (2). All valid deductive arguments beg the question inasmuch as all of their conclusions are implied by their premises.⁹ But a good demonstrative argument, as Aquinas understands it, still leads us from known truth to yet more truth. So he thinks of it as an especially forceful kind of argument, and he holds that such argument is avail able to those who conclude that God exists.

As I noted in chapter 2, some theologians have resisted this conclusion of Aquinas, a prominent example being Karl Barth. And some of their objections to it seem to be anticipated by Aquinas in 1a,2,2.¹⁰

How, one might ask, can it be demonstrated that God exists since it is an article of faith that this is so? And is it not absurd to seek to demonstrate that God exists given that God and creatures are incommensurable (God being infinite and creatures being finite)? Also, what about the (1)–(3) pattern of argument that I have just noted? Does it not seem to rely on an understanding of what Y stands for (mammals in my examples)? Yet should we not accept that we do not know what God is? If we cannot know what God is, however, how can we proceed to a demonstration that God exists? In 1a,2,2, Aquinas raises all of these questions while proceeding to argue that there is nothing wrong in principle with the idea that it is possible to demonstrate that God exists.¹¹

In doing so, he denies that “God exists” is an article of faith (1a,2,2 ad.1). Here he is thinking in terms of the Nicene Creed, and his point is that the creed presupposes that God exists and does not explicitly proclaim that this is so. Readers of 1a,2,2 will perhaps grasp what Aquinas is saying about “God exists” not being an article of faith by noting what he observes in 2a2ae,1,8. There he says that the articles of faith are properly formulated and that the first article of faith is that there is but one God—not that it is true to say that God exists. By contrast to what some philosophers have argued, Aquinas in 1a,2,2 asserts that there is “nothing to stop people from accepting on faith some demonstrable truth that they cannot personally demonstrate.”¹² He does not, however, take this thought to imply that there cannot be a demonstration of the claim that God exists.

In true Barthian fashion, Aquinas agrees that God and creatures are seriously different from each other. He suggests, however, that we need to distinguish between a comprehensive knowledge of God and some knowledge of God. We can know that God exists even if we lack a comprehensive knowledge of what God is (1a,2,2, ad.3). Here Aquinas is saying that a demonstration of the truth of “God exists” does not have to be thought of as including an understanding of what God is. Yet how does Aquinas take himself to be able to argue that it can be demonstrated that God exists, given that we do not know what God is, while providing an argument of the kind (1)–(3) noted above?

Anticipating this question, Aquinas distinguishes between demonstration propter quid (literally, “on account of the whatness”) and demonstration quia (“that”). He says (1a,2,2): “There are two kinds of demonstration. One kind, propter quid, argues from cause to effect and proceeds by means of what is unqualifiedly first. The other, demonstration quia, argues from effect to cause and proceeds by means of what is first so far as we are concerned.”¹³ Here Aquinas is thinking of a propter quid demonstration as an argument that proceeds from an understanding of what something is.

Consider the following argument: (1) Cats are mammals; (2) Smokey is a cat; (3) therefore, Smokey is a mammal. We get to (3) here, Aquinas thinks, on the basis of an understanding of what cats actually are and on the basis of knowing what some particular cat (Smokey) is. Given that we know that cats are mammals, and given that we know that Smokey is a cat, we can readily conclude that Smokey is a mammal.

But now consider this scenario: We try to push a door open but encounter resistance. We shall presumably conclude that something accounts for the door not opening, but we might not know what the something in question is. Nevertheless, we might do our best to say something about the cause of the door not opening based on our knowledge that the door is meeting resistance. Here we might argue along these lines: “Well, something is blocking the door.” And we might then speculate about what the thing in question is based on what we are observing. Here, Aquinas is thinking, we would be engaging in a demonstration quia. We would be arguing from an effect we know well to a cause that we do not know as well. Aquinas thinks that such a demonstration quia might be possible when it comes to arguing philosophically for the truth of “God exists” even though we do not know what God is (something on which he will say more in 1a,1,3).

Note, however, that in taking this line Aquinas holds that we need some initial understanding of the word “God.” I might not know what X actually is; I might not, as Aquinas would say, know what its essence is. But in arguing that X is the cause or explanations of something I am familiar with, I have to work with some nominal definition of X. By “nominal definition” I mean an explanation of what a word means as opposed to an account of what some actually existing thing is by nature. There may be no wizards, but I can explain what the word “wizard” means (as dictionaries do). Thus, for example, suppose I argue that E, which I take to be an effect, is to be accounted for in terms of C, which I take to be the cause of the effect. Suppose, for instance, I argue that a human being with abilities X, Y, and Z accounts for there being a human corpse before me. To prove this I shall have to proceed by working the understanding of C as “human being with abilities X, Y, and Z” into my argument. Accepting this point, Aquinas, in 1a,2,3 goes on to argue for the truth of “God exists” by employing a series of nominal definitions of the word “God” and by using them in a set of causal arguments.

3.3 Arguing for God Causally (1a,2,3)

Aquinas uses the Latin word causa to mean more than we typically signify by “cause.”¹⁴ When we are asking what caused what, we are, so to speak, normally looking for a culprit. Hence, for example, a doctor might wonder what virus is causing the symptoms of a patient. However, and as is indicated by our use of the word “because,” causes might not just be things in the world (like viruses) that act so as to bring about changes in other things (such as healthy human beings). Also, they might not be things in the world that bring about the persist ence of some state of affairs. For example, a crystal glass that I drop might shatter because it is made of crystal as opposed to plastic. My cat might meow because of what it is by nature, and I might be racing to the railway station because I need to catch a particular train. Aquinas has these uses of “cause” or “because” in mind when he distinguishes in 1a,2,2 between demonstrations propter quid and demonstrations quia. In moving to 1a,2,3, however, he is concerned with what I am calling the “culprit” sense of cause. Suppose that I feel a tap on my shoulder. I will react and turn around while looking. Here I am reacting to what Aquinas would have called an “agent cause” or “efficient cause.” I am looking for some particular thing whose action is the tap I feel on my back. Similarly, Aquinas’s Summa Theologiae arguments for the truth of “God exists” are all arguments for the existence of God considered as an agent cause.¹⁵

You may wonder why I have so far spoken of Aquinas as looking to show that “God exists” is true. Should I not have instead said that Aquinas seeks to prove or demonstrate the existence of God? The answer is no since, as we shall see, Aquinas thinks that God’s existence (esse) is not to be distinguished from God’s essence (essentia), which he thinks we cannot know. Yet Aquinas thinks that he can show that “God exists” is a true proposition defensible with an eye on agent causation. This is what 1a,2,3 is chiefly about.

3.4 The Five Ways

1a,2,3 presents what Aquinas calls “five ways in which one can prove that there is a God.” These arguments are famous and have given rise to a huge amount of literature both expository and critical.¹⁶ I cannot here offer a detailed analysis and discussion of them. I shall, therefore, (1) make some general expository points concerning the Ways as a whole, (2) present the text of each Way with brief explanatory notes designed to help you to understand what Aquinas is arguing in them, and (3) briefly draw attention to some familiar criticisms of the Ways while offering some comment on these criticisms.

3.4.1 The Ways as a Whole

As I have noted, Aquinas turns to the business of arguing that “God exists” is true with an eye on certain nominal definitions of the word “God.” In the Five Ways these are: (1) “God” means “an uncaused agent cause of change not itself changed by anything”; (2) “God” means “an uncaused agent cause not itself having an agent cause, that is, a first agent cause”; (3) “God” means “a source of the existence (esse) of all things that can be thought of as necessary beings”; (4) “God” means “the cause of the existence of things displaying perfection to any degree”; and (5) “God” means “one who directs things lacking awareness to their ends.” Presuming that we do not know what God is essentially, Aquinas uses these nominal definitions in the Five Ways so as to provide demonstrations quia of the truth of “God exists.”

This point leads me to stress another directly related to it, one concerning what Aquinas takes himself to have established in his Five Ways. These have sometimes been criticized as “arguments for the existence of God” on the ground that they do not establish that God exists as having all the “attributes” ascribed to God by those who profess belief in God. As I have noted, however, there is a sense in which it would be wrong to read Aquinas as taking himself to be making the existence (esse) of God clear in the Ways, and, as we shall see, Aquinas, in a serious sense, denies that God has any attributes. Also, though sometimes wrongly read as such, the Ways are not Aquinas’s last word in the Summa Theologiae when it comes to what he thinks can be known of God by reason as opposed to revelation. That is why he follows them up with a series of separate arguments for conclusions such as “God is perfect,” “God is good,” “God is eternal,” “God is one,” “God knows,” “God loves,” and “God has power.” Insofar as the Summa Theologiae can be thought of as offering a defense of “God exists,” the defense is not over until 1a,26—actually, it is not really over until the end of 1a,45. The Five Ways are but an attempt to get a certain ball rolling.

A third point worth noting when it comes to the Ways is that none of them are arguing in what we might think of as chronological terms. Theists have sometimes maintained that we can know that God exists since the universe must have had a beginning and since we can reason to God as accounting for the beginning of the universe.¹⁷ Yet Aquinas does not think it possible to demonstrate that the universe had a beginning (as we shall see when we come to 1a,46), and it would be wrong to read the Ways as claiming that God must be responsible only for something arising in the past while not being active in what is happening presently. In 1a,2,3, Aquinas denies that there can be an infinite regress of agent causes, but his denial here presupposes a distinction that he wants to make between a series of causes ordered per accidens and a series of causes ordered per se.

For Aquinas, a causal series per accidens, which he thinks might proceed to infinity, would be referenced by noting, say, that Abraham begat Isaac who begat Jacob who begat Joseph. On this scenario, Abraham is certainly causally related to Joseph by being his great-grandfather. Of course, though, Abraham, being dead at the time, was doing nothing to bring about the conception of Joseph. In the Five Ways, however, the causal series with respect to which Aquinas denies the possibility of an infinite regress is a per se one—a series in which a first cause’s activity runs through a series of effects all of which depend equally on there being such a first cause.¹⁸

Consider the flame on the cooktop of a gas stove, which is heating a pot sitting on it, which, in turn, is heating the water it contains, which, in turn, is heating some spaghetti placed in it. Here the temperature of the pot and the water and the spaghetti can all be traced to the action of the flame, and Aquinas would say that in this case we are dealing with a per se causal series. In the Five Ways, Aquinas starts by noting certain phenomena the occurrence of which at any time, he thinks, depends on the activity of God. He agrees that particular instances of these phenomena might be explicable in terms of things other than God, things that are like them as displaying what they display. He agrees, for example, that a moving ball might cause another ball to move, and that the second ball might cause yet another to move. His point, though, is that there being such phenomena at all cannot be accounted for in terms of something that displays what they exactly display as we seek to account for them. He thinks, for example, that nothing caused to change by something can account for there being things caused to change by other things.¹⁹

Finally, and given what he goes on to say after 1a,2,3, Aquinas takes the Five Ways to be arguing for what cannot be part of the scientifically observable world, the world considered as an object of scientific research. The Ways do not present a series of scientific hypotheses. Aquinas takes them to be suggesting that things with which we are familiar ought to lead us to suppose that there is something that is quite distinct from the world considered as something to be explored scientifically.

3.4.2 The First Way

It is certain, and clear to our senses, that some things in the world undergo change. But anything in process of change is changed by something else. For nothing can be undergoing change unless it is potentially whatever it ends up being after its process of change—while something causes change insofar as it is actual in some way. After all, to change something is simply to bring it from potentiality to actuality, and this can only be done by something that is somehow actual: thus fire (actually hot) causes wood (able to be hot) to become actually hot, and thus it changes and modifies it. But something cannot be simultaneously actually x and potentially x (something actually hot, for instance, cannot also be potentially hot, though it can be potentially cold). So, something in process of change cannot itself cause that same change. It cannot change itself. Necessarily, therefore, anything in process of change is changed by something else. And this something else, if in process of change, is itself changed by yet another thing; and this last by another. But there has to be an end to this regress of causes, otherwise there will be no first cause of change, and, as a result, no subsequent causes of change. For it is only when acted upon by a first cause that intermediate causes produce change (if a hand does not move the stick, the stick will not move anything else). So, we are bound to arrive at some first cause of change that is not itself changed by anything, which is what everybody takes God to be.²⁰

Here note:

(a) The second sentence quoted above reads in Aquinas’s Latin Omne autem quod movetur ab alio movetur, which can also be translated as “Anything changed is changed by something else.” Because of ambiguity concerning Latin usage when it comes to the verb movere (“to move”), scholars have asked whether the First Way is starting from the fact that some things are passively acted on as they change (are changed) or starting from the fact that things just go through a process of change (are changing). You might think that “everything changed is changed by something else” is so obviously true that Aquinas cannot go on to argue for its truth as he does in the First Way. But, of course, something can be changed by itself, as when I cut myself. And one might well construe the First Way as starting from the fact that things are changed (passive) and not from the fact that things change (intransitive).

(b) Like each of the Five Ways, the First Way begins with what we might callan observational premise. This is that some things in the world undergo change (motus). By motus Aquinas means real change in general.²¹ The First Way has often been described as an argument for there being an unmoved mover. “Motion,” however, is commonly taken these days to refer only to local motion, and we need to realize that Aquinas takes motus to include not just change of place but also change of quantity, as when I put on weight, or quality, as when I acquire a suntan.²² The First Way is arguing that instances of change in these senses depend on something bringing the change about.

(c) At the center of the First Way’s argument is the claim that motus occurs as something comes to be what it is not to start with because something that is actually able to account for this is actually doing so. In making this claim, Aquinas distinguishes between something being potentially thus and so and something being actually thus and so. Here he is distinguishing between (1) something now thus and so though able to be different, and (2) something just being real (aliquid ens actu—“some real thing”). He would say, for example, that, though I am actually sitting at a desk I could be standing in my kitchen. Then he would say that my coming to be standing in my kitchen is brought about by something real.²³ He would also say that something potentially thus and so coming to be actually thus and so is not explicable in terms of what the thing is to start with, that X coming to be F is not explicable with reference to a description of what X is before it comes to be F. He certainly thinks that a description of X as being F can be a genuine description of X. But he does not think that it accounts for X coming to be F having previously been not F. Here he looks for something distinct from X as not F, and, we should realize, in spite of the heat example he uses in the First Way, he does not thereby commit himself to the principle that whatever accounts for X coming to be F must itself be F in the way X is F once it has come to be F. He does not, for ex ample, think that if I break your arm I must myself have a broken arm. What he thinks is that if you end up with a broken arm, that will be because of something (or maybe more than one thing) that actually exists and has the power to bring it about that your arm is broken.

(d) In the First Way, Aquinas denies that there can be an infinite regress of changers. We should remember that the infinite series that he is here denying is a series ordered per se.

3.4.3 The Second Way

We find that there is an order of efficient causes in the observable world. Yet we never observe, nor ever could, something efficiently causing itself. For this would mean that it preceded itself, which it cannot do. But an order of efficient causes cannot go back infinitely, for an earlier member in it causes an intermediate, and the intermediate causes a last (whether the intermediate be one or many). If you eliminate a cause, however, you also eliminate its effects. So, there cannot be a last cause, nor an intermediate one, unless there is a first. If there is no end to the series of efficient causes, therefore, and if, as a consequence, there is no first cause, there would be no intermediate efficient causes either, and no last effect, which is clearly not the case. So we have to posit a first cause, which everyone calls “God.”²⁴

Here note:

(a) When talking about efficient causes in the Second Way, Aquinas starts from the premise that there are agent causes in the world, causes that, just by being so, have effects. He is alluding to the fact that, for ex ample, we can be clearly aware that the pages of a book I am reading are being turned over by me, or that barbers cut people’s hair. Since examples such as these evidently involve instances of what Aquinas would call motus, the concern of the Second Way clearly overlaps with what the First Way talks about, though, by contrast to the First Way, the Second Way proceeds by reference to observable causality taken itself as an effect to be explained by reference to a further cause, and not from a non-causal effect to a cause.

(b) Aquinas takes it to be obvious that there is agent causation in the world. You should realize, however, that he would not take all such causation to involve the bringing about of a change in something. You might think that a picture on a wall stays in position because it is supported by what it is hanging on, and you may think that what it hangs on stays there because it is supported by the wall into which it is driven. And Aquinas would think the same. So the Second Way is not just concerned with causes of change but also with causes of a status quo obtaining by virtue of something else.

(c) In the Second Way, Aquinas is arguing for a “first cause,” and it has been suggested that he is, therefore, arguing that there has to be a cause for the sheer existence (esse) of anything that exists, as he does in De Ente et Essentia,4. There he argues (1) that understanding what existing things are by nature does not come with the understanding that some particular things exist (that, for example, understanding what cats are does not guar antee that one understands that my cat or any particular cat exists), and (2) that we need to account for there being things that do not exist by nature. But Aquinas is not arguing along these lines in the Second Way, though he is evidently concerned with things coming to be somehow, if only because he would take it that coming to be thus and so because of an agent cause is always a matter of something coming to a way of being or having its way of being maintained. Like all of the Five Ways, the Second Way begins with an observational premise and is not concerned, as is the De Ente et Essentia, with maintaining (without critical reference to an observational premise) that the existence of things other than God can be distinguished from their natures and that there has to be a cause of such things existing on pain of an infinite regress of causes. What he claims in the Second Way is that we observe agent or efficient causes to be ordered to effects.²⁵ In other words, thinks Aquinas, there evidently are effects of efficient or agent causes and, therefore, efficient causes of effects.

(d) Given the observational nature of the start of the Second Way, and given that Aquinas takes observable agent or efficient causation to include cases where change in one thing comes about by virtue of something else, the Second Way can be read as parallel to the reasoning of the First Way while concentrating (though not exclusively) on causes of motus rather than on motus considered as an effect.²⁶

(e) In the Second Way, Aquinas appears to presume that nothing can be its own efficient cause without being prior to itself. As John Wippel observes, he seems to be thinking that “for something to cause itself efficiently, it would have to exist in order to cause (itself), and yet would not exist, insofar as it was being caused.”²⁷ The reasoning here is comparable to or, indeed, exemplified by that of “Nothing can itself account for the warmth it is getting from something else.” You might, perhaps, think that something can be or can come to be while lacking what Aquinas thinks of as an agent or efficient cause. In the Second Way, however, Aquinas is not arguing otherwise; indeed, he is arguing that something can be while lacking an agent cause. His point about nothing being its own efficient cause amounts to a claim concerning what has to be the case only of what is efficiently caused (a change in something owing to something, or the maintaining of something’s physical position owing to something, and so on). When it comes to this, he thinks, another is required.

(f) In the Second Way, Aquinas denies that there can be an infinite regress of efficient causes. We should remember, however, that the infinite series that he is here denying is a series ordered per se.

3.4.4 The Third Way

Some of the things we encounter are able to be or not to be, for we find them generated and perished (and, therefore, able to be or not to be). But not everything can be like this. For something that is capable of not being, at some time is not. So, if everything is able not to be, at some time there was nothing in the world. But if that were true, there would be nothing even now, for something that does not exist is only brought into being by something that does exist. Therefore, if nothing existed, nothing could have begun to exist, and nothing would exist now, which is patently not the case. So, not everything is the sort of thing that is able to be or not to be. There has got to be something that must be. Yet a thing that must be either does or does not have a cause of its necessity outside itself. And just as we must stop somewhere in a series of efficient causes, so we must also stop in the series of things which must be and owe this to something else. This means that we are forced to posit something which is intrinsically necessary, owing its necessity to nothing else, something which is the cause that other things must be.²⁸

Here note:

(a) The observational premise in the Third Way is “Some things come to be generated and some things perish.” Aquinas’s reference to generation and perishing here seems to imply that he is thinking of examples such as “People come to be as other people mate” or “People die.”

(b) The coming to be and passing away to which Aquinas refers in his Third Way involves what he would call “substantial change.” For him, a substantial change occurs when a genuine substance ceases to exist because of the activity of something other than it, as when a cat is put to sleep by a vet.²⁹ Strictly speaking, Aquinas thinks, a substantial change is not a change undergone by something that exists throughout the course of the change in question—it is not an “accidental change.” He recognizes, for instance, that, while my cat exists through the changes it undergoes when I clip its claws, it does not exist before its generation and after its demise. Yet he also thinks that some changes in the world amount to a coming to be and a passing away. There are, he believes, more changes in the world than what he would call “accidental changes.” When I have clipped my cat’s claws, it has undergone a change, but it has survived as the cat that it is. What if I kill it, however? It would seem that a change of some sort has occurred, but not one of which my cat can tell the tale. And what if my cat breeds and produces kittens? Again, it would seem that a change of some sort has occurred, but not a change in the kittens, for this is a change amounting to their coming to exist. It is with an eye on such examples that Aquinas quite generally in his writings refers to “substantial change,” which he takes to occur as genuine substances come into being and pass away in the context of the material world.

(c) Some readers of Aquinas have taken his Third Way to argue that God, considered as the one and only necessary being, has to exist in view of the fact that contingent things exist. These readers have interpreted the Third Way as holding:

(1) some things are contingent things;

(2) all contingent things require a cause to account for their existence;

(3) so there has to be a single non-contingent necessary thing accounting for the existence of all contingent things;

(4) so God exists.

This argument seems dubious since each contingent thing might have a cause of its existence without there being a single cause of the existence of all contingent things.³⁰ Be that as it may, the argument I have just noted is not that of the Third Way. Aquinas does not use the word “contingent” in the Third Way. He focuses on things able to be or not to be in that they come to be and perish.³¹ And he clearly accepts that there might be more than one necessary being.

(d) In the Third Way, Aquinas says, “Something that is capable of not being at some time is not (quandoque non est). So if everything is able not to be, at some time there was nothing in the world.” Interpreters of Aquinas have disagreed about how to understand his reasoning here. Some have taken him to be arguing that if everything is perishable, then everything would have perished by now.³² Others have read him as claiming that if everything is a generated thing, there would be nothing now since a series of generated things has to be accounted for with respect to what is not itself generated. The first reading here seems dubious for two reasons. First, it leaves us supposing that Aquinas is fallaciously arguing that if everything is perishable, there has to be a single time at which everything has perished—while we might reasonably suppose that the fallacy involved here would have been obvious to someone of Aquinas’s intellectual stature.³³ Second, the reading appears to attribute to Aquinas the view that things able to be or not to be have existed from an infinite past time, while Aquinas does not articulate this view in the Third Way, and we know that he did not think it possible to establish philosophically that the world has existed for an infinite past time.³⁴ So it seems more likely that in the Third Way Aquinas is focusing on generation rather than perishing and arguing (a) that things that are generated come to be having not existed before they came to be, and (b) that if everything is a generated thing, there would be nothing now. On this reading Aquinas would be saying that anything generated depends on a cause of its coming to be and that there could not be any generated things unless there were something acting causally while not itself being something generated. In support of this reading we might note that in the Third Way, and as part of his argument to the effect that not everything is able to be or not to be, Aquinas insists that “something that does not exist is only brought into being by something that does exist.”

(e) Unlike some philosophical texts, the Third Way, as I have already noted, is not arguing that God exists as the only necessary being there is. Having maintained that not everything is able to be or not to be, Aquinas turns to things not able to be or not to be (things that are, in his terminology, necessary) while clearly presuming that there might be more than one of them. And, apart from what he says in the Third Way, we know that Aquinas believed that there were many necessary beings, that is, beings not generated or perishable in the course of nature—such as angels and human souls. So Aquinas does not take himself in the Third Way to have arrived at the conclusion that God exists merely by establishing that not everything is able to be or not to be. And he goes on in the Way to ask whether a series of things not able to be or not to be can exist without there being something both notable to be or not to be and existing uncaused. He argues that a series of things not able to be or not to be has to depend on something that exists uncaused. As he puts it: “Just as we must stop somewhere in a series of efficient causes, so we must also stop in the series of things which must be and owe this to something else.”³⁵

3.4.5 The Fourth Way

We find some things to be more or less good, more or less true, more or less noble, and so on. But we speak of various things as being more or less F in so far as they approximate in various ways to what is most F. For example, things are hotter and hotter the closer they approach to what is hottest. So, something is the truest and best and most noble of things, and hence the most fully in being. For, as Aristotle says, the truest things are the things most fully in being. But when many things possess some property in common, the one most fully possessing it causes it in the others. To use Aristotle’s ex ample, fire, the hottest of all things, causes all other things to be hot. So, there is something that causes in all other things their being, their goodness, and whatever other perfection they have, and we call this “God.”³⁶

Here note:

(a) The observational premise of the Fourth Way might strike some readers as not being any such thing. For do we observe that some things are more or less good, true, noble, and so on? In the Fourth Way, Aquinas seems to begin with a premise with an evaluative component built into it. Some people, though, have wanted to distinguish sharply between facts and values so as to suggest that none of our descriptions of observable things in the world entail that these things should be evaluated in some particular way. They have suggested, for example, that, from what we know of John by watching him, we cannot conclude that he is a good man. Aquinas, however, never employs such a fact-value distinction. When speaking of things in the world he always takes them to be gradable (in principle, anyway, and albeit with qualifications) with an eye on what we can see them to be empirically. He would say, for example, that a good cat is not just well behaved (by some standards of being well behaved that we might have), but objectively healthy.³⁷ And Aquinas thinks of health as something detectable by our senses. So he takes the first premise of his Fourth Way to be an observational one. He regards it as, for example, truly asserting that we can literally see that some things display more goodness than other things.

(b) To understand the Fourth Way one needs to realize that Aquinas regularly takes being, truth, and goodness to be related in a serious way.³⁸ For him, something that has being is always to some extent good. He also thinks that things that exist and are, therefore, good in some way can be thought of as true in that they possess what our minds can latch onto as intelligible. With these thoughts in mind, Aquinas can say, as he does in the Fourth Way, that things are good and true. We would not naturally assert that a cat, say, is true, though we readily refer to true propositions or statements. But taking truth to amount to a “conformity” of thing and intellect, Aquinas has no problem in supposing that we grasp truth as we latch on to what is. And he would have no problem in supposing that to latch onto the truth about some cat (or whatever) is to be presented not just by a true proposition or statement but by something that exists and can, therefore, be said to be true (and good).³⁹ Aquinas will also say that something can be better (more good) than something else, more true than something else, and more in being than something else. For Aquinas, something is good insofar as it exhibits actual perfections in some way— this amounting to it having being to a certain extent—and with this thought in mind he will say that if X is better than Y, then there is more present (more being) in X than in Y. Since he holds that truth and being can be thought of as seriously coinciding, Aquinas will assert that something can be more true than another thing insofar as it possesses more than another thing does and is, in this sense, better than it. In the Fourth Way, Aquinas is drawing on all of these notions, odd or obvious as you might take them to be.

(c) The Fourth Way starts from the claim that things in the world display different degrees of perfection. Given what I have just noted, we should not take it just to be noting that we can grade things within a certain class. We obviously do exactly this. We say, for example, that cat 1 is healthier than cat 2 and that cat 3 is healthier than cats 1 and 2. As the ex ample of heat that he gives indicates, Aquinas is allowing for this kind of comparative evaluation in the Fourth Way. But the Fourth Way is also working with the thought that comparisons when it comes to perfections can be made with respect to things of different kinds. In particular, it is assuming that goodness, which can be had in different degrees by things of one kind, can be had to a greater degree by something not belonging to that kind. Since Aquinas thinks that something is good insofar as it possesses reality, insofar as it exists as it does, he thinks that where we have more that is real we have more goodness. He does not take “good” to signify a distinct property as, for example, does “plastic” in “plastic bag.” Nor does he take “exists” (“has being”) to signify such a property. But he does think that being good involves being or being actual. So he holds that even though two things, an angel and a mouse, for instance, might not belong to one kind, they can be comparatively graded when it comes to perfection. Aquinas would say that there is more (being) in angels than in mice. He would therefore say that angels are more perfect than (better than, more good than) mice. This means that the Fourth Way should not be construed as, for example, arguing that if some cat is good, and if another cat is better than it, there has to be a cat that is the best cat of all.

(d) Like all the Five Ways, the Fourth Way presents a causal argument for the existence of God as an agent or efficient cause, and its crucial causal move comes in the words “When many things possess some property in common, the one most fully possessing it causes it in the others.” What does Aquinas mean when saying this? He does not mean that, for example, if A, B, and C are green, then they are all caused to be green by something that is supremely green. He means that if different things can be thought of as being thus and so, their being thus and so has to be accounted for in terms of something that has in it the wherewithal to bring it about that they are thus and so, something whose nature is reflected in what it brings about. As we can see from texts like his De Principiis Naturae, Aquinas holds that the effects of agent causes resemble their causes, but he does not think that they have to look like their causes. Rather, he maintains, agent causes account for what they produce by being what they are and, accordingly, explaining the coming to be of what they account for. I might ask “Why did my cat get sick?” Research might show that my cat licked up some disinfectant that I spilled on my kitchen floor. Given this scenario we would say “Well, of course, given that the cat consumed disinfectant, it is only to be expected that it would get sick.” But why would we say this? I presume that we would do so because of our knowledge of disinfectant and the changes it brings about in different things, and Aquinas would agree with us. He would, however, add that our knowledge of disinfectant would here have to amount to a knowledge of what it essentially is and not just a recognition that disinfectant has often produced thus and such effects in things. To note that cats who drink disinfectant regularly become sick does not explain why any cat becomes sick having drunk disinfectant. It merely reports what we have become used to experiencing, and Aquinas would say that understanding why an agent cause has the effect it does depends on understanding the nature of the cause (not to mention the things on which it is acting). Only when one has developed this kind of understanding, thinks Aquinas, does one know why certain effects show their causes in action and why the effects in question are only to be expected. When saying that effects resemble their agent causes and vice versa, he means that agent causes are somehow reflected in their effects. Aquinas thinks that agent causes sometimes produce what looks just like them, and in the Fourth Way he gives the example of fire being hot as things affected by it are hot. But he does not think that this is always the case, as you need to recognize when reading the Fourth Way.

(e) As I have noted, the Fourth Way starts with reference to degrees of goodness or perfection, and it concludes by saying that goodness and being in things we encounter require a cause. The goodness and being of things in the world, Aquinas thinks, have to be efficiently caused by something the goodness and existence of which are not derived from any agent cause. Given the way in which he thinks that to be good is to be somehow, what this means is that, in the Fourth Way, Aquinas is effectively asking “How come something rather than nothing?” while maintaining that there is an answer to this question, albeit one that we cannot understand. As we shall see, this thought dominates the reasoning given in the Prima Pars.

3.4.6 The Fifth Way

The Fifth Way is based on the guidedness of things. For we see that some things that lack intelligence (i.e., material objects in nature) act for the sake of an end. This is clear from the fact that they always, or usually, act in the same way so as to achieve what is best (and therefore tend to a goal and do not reach it by chance). But things lacking intelligence tend to a goal only as directed by one with knowledge and understanding. Arrows, for instance, need archers. So, there is a being with intelligence who directs all natural things to ends, and we call this being “God.”⁴⁰

Here note:

(a) Some people have argued that the world contains designed objects that demand explanation with reference to a celestial designer not itself part of the world. An especially famous example of someone thinking along these lines is William Paley (1743–1805). In Natural Theology, he compares various naturally occurring things to watches while arguing that they are made up of parts that seem put together to achieve a definite result. “Every indication of contrivance” and “every manifestation of design” that can be found in a watch, he says, “exists in the works of nature; with the difference, on the side of nature, of being greater and more.”⁴¹ Though some readers of it seem to have thought otherwise, however, the Fifth Way is not an “argument from design” in Paley’s sense. It does not appeal to vast cosmic evidence of design not produced by any human being while produced by a nonhuman designer. Nor is it saying that the world is a single, huge designed object. Rather, it is noting that some, and only some, things in the world “act for the sake of an end.” Aquinas is saying that, forgetting about anything we might know about human behavior, there are some things in the world that can be thought of as goal-directed in their activity, and his argument is that the goal-directed activity of these things has to be due to a directing (nonhuman) intelligence of some kind.

(b) Why does Aquinas say that certain things “act for the sake of an end”? The answer to this question can be found in his claim that some things that lack intelligence “always, or usually, act in the same way so as to achieve what is best” without doing so “by chance.” Aquinas believes that chance events occur since (as he says in 1a,116 and 2a2ae,95,5) an event might have no single cause accounting for just that event. My happening to be killed by the branch of a tree that falls on me as a gust of wind strikes it just as I pass under it would, for Aquinas, be an instance of a chance event. But what about the fact that female cats regularly and instinctively suckle their newborn kittens and thereby help them to become healthy cats? Or what about the fact that my heart regularly functions so as to circulate my blood and, accordingly, keep me alive? These are the kinds of examples that Aquinas seems to be thinking of in the Fifth Way. In instances like these, he perceives goal-directed activity, but not activity that is goal-directed because a human being is at work.

(c) When we seek to account for what we encounter, thinks Aquinas (and if we read him as though he were speaking English), we are always looking for an account that begins with the word “because,” as in “This can be accounted for because of that.” In other words, we are looking for causes most of us these days would mean when referring to a cause. I presume that when we look for causes we are normally looking for what Aquinas calls an “agent” or “efficient” cause (as in “Who killed Fred?”). Following Aristotle, however, Aquinas says that there are four kinds of cause: efficient, material, formal, and final, and its final causality that is the focus of the Fifth Way. Although it concludes with reference to God as an agent cause, the Fifth Way is also much concerned with final causation in that it begins with the claim that there is goal-directed activity even on the part of things different from John in that they are not reasoning or thinking individuals. Such things, Aquinas holds, have goal-directed tendencies, albeit ones that are sometimes frustrated. In this sense, he thinks, there are non reasoning things that aim at certain goods, and, he maintains, such aiming is derivative from what has knowledge or understanding. Hence, the ex ample he uses of an arrow shot by an archer.

3.5 Critical Responses to the Five Ways

How cogent is Aquinas’s reasoning in the Five Ways? I cannot note all that has been said in criticism of them (of which there is a lot), but here are some arguments that have often been leveled against them:

(a) The arguments fail because they do not succeed in showing that God exists. At best, they only show that there is an unchanged changer, an uncaused agent cause, a necessary being not caused to exist by anything, a source of there being things with degrees of perfection, and a cause accounting for things in nature acting for ends. But arguments purporting to show that God exists must establish that God is, for ex ample, one, omnipotent, omniscient, and any number of other things. Since the Five Ways do not do this, they fail as arguments for the conclusion that God exists.

(b) All of the Ways rest on dubious claims. The First Way, for instance, asks us to believe that anything undergoing change so as to become F is being changed by something else that is F. But this principle is obviously false since, for example, one does not need to be dead to commit murder. Again (so it has been argued), the First Way was in effect refuted by Isaac Newton (1642–1727) whose first law of motion states that, because of the principle of inertia, an object will just continue to move in a straight line in absolute space unless interfered with.

(c) We have no good reason to think that any causal series has to have something uncaused at the start of it.

(d) All of the Five Ways depend on a logical fallacy that can be illustrated by the example “All roads lead somewhere; so there is some (one) place to which all roads lead”—a fallacy sometimes referred to as “the quantifier shift fallacy.” For instance, the First Way fallaciously argues that since each instance of motus has an agent cause, there is one agent cause accounting for each instance of motus. And the Second Way argues in a comparable way with an eye on agent causality, while the Third Way fallaciously maintains that, since everything perishes at some time, there must be a time at which everything has perished. With respect to the Fourth and Fifth Way, one can object to them since they fallaciously maintain that (1) if the perfection exhibited by one thing depends on a cause, there is one thing that accounts for all things exhibiting degrees of perfection, and (2) if something accounts for the tending to an end of something lacking awareness, there is some one thing accounting for the tending to an end of all things lacking awareness.

(e) In the Five Ways, Aquinas always seems to assume that we should be looking for agent causes. But why should we not take various things we know about to be “just there” with no causal questions arising from them being so? Why not suppose, for instance, that something undergoing change is just changing? Or why not suppose that something in the world can just exist without us having to look for a cause of its existing? And why not settle for the conclusion that things lacking awareness tend to an end because that is just what they do? In response to these criticisms I can imagine Aquinas saying:

(1) The Five Ways do not purport to establish that God exists as being all that those who believe in God take God to be. They purport to establish only that there is something unchanged accounting for change, some un caused agent cause, something necessary the existence of which is underived, something accounting for there being things that exist and are good, and something accounting for goal-directed activity on the part of things lacking intelligence.

(2) The First Way does not invoke the premise that only what is F can bring it about that something comes to be F, that, for example, one needs to be dead in order to commit murder. And the principle of inertia should not be thought to refute the point that something coming actually to be what it was before only potentially does not bring itself into the state of actuality at which it arrives.

(3) While a per accidens series of agent causes might proceed to infinity, this cannot be so when it comes to a per se series.

(4) None of the Five Ways displays a quantifier shift fallacy. Their concern is to argue that, given certain things we encounter, we need to suppose that there is something accounting for them that is distinct from them.

(5) The quest for an agent cause (or for several agent causes) is legitimate when we are concerned with what does not have to be the case considered as what it is, what it does, or what is happening to it.

At least, I suspect that Aquinas would make these points and go on to develop them in response to the criticisms of the Five Ways noted above. Whether or not he might ultimately be successful in pressing them, however, is not a question that I can try to discuss now. Instead, I must content myself with noting that, having arrived at the end of 1a,2, Aquinas takes himself to have said enough to show that we have good philosophical reason to think that God, understood in the senses specified in the Five Ways, exists. As he moves on, he proceeds to ask what God actually is and how our talk about God can be thought of as latching on to God’s nature. Let us see what he has to say about this.

1.       When I say “much-quoted” I am really thinking of 1a,2,3, in which Aquinas provides five arguments for believing that God exists. The text of this article has been reprinted in translation countless times. And it is often thought of as the best that Aquinas has to offer when it comes to the question “Does God exist?” In the present volume I try to introduce the text with an eye to its context.

2.       Aquinas defends this position in Book I of his commentary on the Sentences and Book I of his Summa Contra Gentiles.

3.       This line of thinking can be found in the writings of some of Aquinas’s contem poraries, notably St. Bonaventure (1217–1274). Cf. Question 1, Article 1 of his De Mysterio Trinitatis (Disputed Questions on the Mystery of the Trinity). For an English edition of this text, see Saint Bonaventure’s “Disputed Questions on the Mystery of the ture defends all of the positions discussed and rejected by Aquinas in 1a,2,1.

4.       For an English translation of the Proslogion, see Brian Davies and G. R. Evans (eds.), Anselm of Canterbury: The Major Works (Oxford University Press: New York, 1998). For Anselm and the Ontological Argument, see my “Anselm and the Ontological Argument” in Brian Davies and Brian Leftow (eds.), The Cam bridge Companion to Anselm (Cambridge University Press: Cambridge, 2004). For an account and discussion of the Ontological Argument from Anselm onward, see Graham Oppy, Ontological Arguments and Belief in God (Cambridge University Press: Cambridge, 1995).

5.       Cf. Graham Oppy, Ontological Arguments and Belief in God.

6.       Davies and Leftow, 2006, 20. Aquinas does not quote Anselm in connection with this argument, but he must have been familiar with Anselm’s argument.

7.       Gaunilo (a monk of the Abbey of Marmoutiers in France) replied to Anselm in a text called Quid ad haec respondeat quidam pro insipiente (“A Reply to the Fore going by a Certain Writer on Behalf of the Fool”). Anselm replied to Gaunilo in Quid ad haec respondeat editor ipsius libelli (“A Reply to the Foregoing by the Author of the Book in Question”). To understand how Anselm conceived of his “ontological argument” one definitely needs to read his reply to Gaunilo. But this is something to which Aquinas never refers.

8.       Cf. H. D. Lewis, Philosophy of Religion (The English Universities Press Ltd: London, 1965), chapter 14. Here Lewis speaks of knowing God on the basis of “cognition,” “insight,” and “intuition.” He sums up his position by saying that God “is closer to all things than distinct finite things ever are to one another” while adding “This we see, not as inference, but in one insight or leap of thought” (146).

9.       Cf. P. T. Geach, Reason and Argument (Basil Blackwell: Oxford, 1976), 18: “Bad logic books list ‘begging the question’ as a fallacy. This objection, however, is a mere confusion, and in the court of logic it should be denied a hearing: if the conclusion really is implicit in the premises, then the argument is logically as good as it can be—the conclusion really and indefeasibly follows from the premises.” It might be suggested that people who know the premises of a valid argument can have no use for the argument since they already know its conclusion. As Geach observes, however: “This protest forgets that a man may know each premise, but never happen to think of the two premises together and draw the obvious conclusion.” Moreover, even with the premises before them, people vary very much in their natural or acquired ability to derive conclusions from them; having the premises is no guarantee that they will know how to derive the right conclusion” (18–19).

10.    I mention Barth again here since he is an especially famous modern theologian with whom some readers of this book might already be familiar. But in 1a,2,2, Aquinas, of course, is writing with an eye to what he knew some of his predecessors and contemporaries thought.

11.    With respect to not knowing what God is, Aquinas makes reference to St. John Damascene (ca. 676–749). I presume that he is alluding to Damascene’s De Fide Orthodoxa, 1,4, which emphasizes the incomprehensibility of God. Aquinas definitely takes Damascene to be a Christian author to be read as authoritative.

12.    Davies and Leftow, 2006, 23. For a text famously concluding that “it is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence,” see W. K. Clifford, “The Ethics of Belief,” in W. K. Clifford, Lectures and Essays, 2nd ed., edited by Leslie Stephen and Frederick Pollock (Macmillan: London, 1886). This essay has been frequently reprinted. It can be found in an edited form in my Philosophy of Religion: A Guide and Anthology (Oxford University Press: Oxford, 2000).

13.    Davies and Leftow, 2006, 23 (with emendation).

14.    For a good essay on Aquinas on “cause,” see Michael Rota, “Causation,” in Brian Davies and Eleonore Stump (eds.), The Oxford Handbook of Thomas Aquinas (Oxford University Press: Oxford, 2011), 104–114.

15.    In all of the writings in which he discusses the matter, Aquinas takes arguments for the truth of “God exists” to be like this. To my knowledge, the best available account of Aquinas’s many arguments for the truth of “God exists” is Fernand Van Steenberghen, Le Problèm de l’existence de Dieu dans les Écrits de S. Thomas D’Aquin (Éditions de l’institute supérieur de philosophie: Louvain-La-Neuve, 1980).

16.    For a good account of the Five Ways, I would strongly recommend chapter 12 of John Wippel, The Metaphysical Thought of Thomas Aquinas (The Catholic Uni versity of America Press: Washington, D.C., 2000). An often-quoted critical discussion of the Five Ways is Anthony Kenny, The Five Ways (Routledge & Kegan Paul: London, 1969). For a helpful corrective to Kenny’s book, see Lubor Velecky, Aquinas’ Five Arguments in the Summa Theologiae 1a 2,3 (Kok Pharos: Kampen, 1994); and C. F. J. Martin, Thomas Aquinas: God and Explanation (Edinburgh University Press: Edinburgh, 1997). All of the volumes just noted point readers in the direction of other secondary literature on the Ways.

17.    This is the approach to God expressed by the claim “Something must have started it all.” For a development of it, see William Lane Craig, The Kalām Cosmological Argument (Macmillan: London and Basingstoke, 1979).

18.    Aquinas sometimes speaks of the effects of the first cause in a per se causal series as being “instruments” of it. Cf. his commentary on Aristotle’s Physics, 8,9. Also cf. De Veritate, 27,4.

19.    For a good account of Aquinas’s distinction between causal series ordered per se and causal series ordered per accidens, see Scott MacDonald, “Aquinas’s Parasitic Cosmological Argument” (Medieval Philosophy and Theology, vol. 1, 1991).

20.    Davies and Leftow, 2006, 24–25.

21.    By “real change” I mean a genuine modification of an existing thing (as, e.g., is someone’s putting on weight or sailing from the United Kingdom to the United States). We sometimes seem to ascribe change to things where the change is not real change in this sense. Thus, for example, we may say “Mary came to be ad mired by Paul” without implying that Mary herself underwent any real change. This second sense of “change” is not what Aquinas is thinking of in the First Way.

22.    This is not obvious from the text of the First Way (which only invokes an ex ample of local motion). But note Aquinas’s commentary on Book V of Aristotle’s Physics (Lecture 2) in which the point is made clearly. The English word change can be rendered into (Aquinas’s) Latin by both motus and mutatio. In his Physics commentary, Aquinas allows for mutatio that is not motus while referring to what he calls substantial change, which he thinks of, not as a change in an actually existing thing but as the coming into existence of something or the passing out of existence of it (e.g., the generation or death of a human being).

23.    I use this example in order to bring out the fact that Aquinas does not in general think that all change in a subject is brought about by what is quite different from the subject. I might be frog-marched into my kitchen by someone, but my coming to be standing in my kitchen might also be explicable with reference to the movements of my legs, which are parts of me.

24.    Davies and Leftow, 2006, 25.

25.    In the Second Way Aquinas does not give any concrete examples of what he is thinking of when he speaks of efficient causes and effects ordered in series. But he is definitely thinking in terms of examples such as I give (while allowing that a number of efficient causes and effects of efficient causes might be observed all together [as it were])—as, when it comes, say, to a hand moving a stick that moves something else (an example that Aquinas does give in the First Way).

26.    Anthony Kenny makes this point in his The Five Ways (Routledge & Kegan Paul: London, 1969), 35–36. In his Thomas Aquinas: God and Explanations, C. F. J. Martin speaks of the Second way as a “generalization” of the First Way (146).

27.    Wippel, The Metaphysical Thought of Thomas Aquinas, 459.

28.    Davies and Leftow, 2006, 25–26.

29.    Basically, Aquinas takes a substance to be a naturally occurring thing, object, or being (as opposed to an artifact). This sense of “substance” can be found in the writings of Aristotle. According to this sense, dogs and cats, for example, would be substances (though computers or telephones would not). For more on this, see John F. Wippel, The Metaphysical Thought of Thomas Aquinas (cited above).

30.    For a discussion of people wrongly interpreting Aquinas as saying that there has to be only one necessary being, see Patterson Brown, “St Thomas’ Doctrine of Necessary Being,” reprinted in Anthony Kenny (ed.), Aquinas: A Collection of Critical Essays (University of Notre Dame Press: Notre Dame, 1976).

31.    When referring to contingency, some philosophers have said that there are statements that are contingently true because they are not true of logical necessity. On this account, “the Eiffel Tower exists” is a logically contingent statement while “all triangles have three sides” is a logically necessary one. With this distinction in mind it has also been suggested that there is a corresponding difference when it comes to things that exist contingently and things that exist necessarily—the idea being that something existing contingently is something the existence of which can be denied without self- contradiction while the existence of something necessary cannot be denied without self-contradiction. As we have seen, Aquinas thinks that the proposition “God does not exist” can be denied without the person propounding it being guilty of self-contradiction.

32.    An argument to this effect can be found in II,1 of The Guide of the Perplexed by Moses Maimonides (1135–1204). This is a text with which Aquinas was familiar.

33.    The fallacy is sometimes called “the quantifier shift fallacy” and is illustrated by the argument “All roads lead somewhere, so there is some (one) place (e.g., Rome) to which all roads lead.”

34.    The interpretation of the Third Way to which I am now referring supposes that Aquinas is assuming that if the world has existed from infinity, perishable things in it would all have perished by now. For Aquinas clearly denying that philosophy can establish that the universe had a beginning, see John Wippel, Metaphysical Themes in Thomas Aquinas, chapter 8. Aquinas develops this case in his De Aeternitate Mundi (On the Eternity of the World). Cf. also Summa Theo logiae, 1a,46,2.

35.    I defend the second reading to which I here refer in “Aquinas’s Third Way,” New Blackfriars 82, no. 968 (October 2001). Note that in his Summa Contra Gentiles (I,15), Aquinas offers an argument strikingly similar to what we find in the Third Way. This argument is clearly concerned with things coming to be rather than things coming to pass away.

36.    Davies and Leftow, 2006, 26.

37.    I suspect that Aquinas would be happy to say that a badly behaved cat (by a criterion of being well behaved that we might have when thinking about cats) might be a very good cat (because it is healthy). Aquinas frequently takes “good” to be an adjective only understandable when it comes to the work it is doing as predicated of something in particular. We might ask “Is X good?” Abstracting from things that he wants to say about God’s goodness, Aquinas would reply, “I cannot answer the question until I know to what you are referring by ‘X.’” He would mean that we commend things as being good for different reasons and depending on what things we are talking about and under what category we place them—that, for example, we might say that Fred is a good parent but a bad doctor. When thinking about things in the world, Aquinas takes “good” to be an attributive adjective and not a predicative one. On this distinction, see P. T. Geach, “Good and Evil,” Analysis 17 (1956).

38.    One can see him doing so in, for example, De Veritate, 1,1. According to Aqui nas, being, truth, and goodness are “convertible”—meaning that something exists only insofar as it is somehow true and good.

39.    Again, cf. De Veritate, 1,1.

40.    I quote here from Davies and Leftow, 2006, 26 (with some emendation).

41.    Cf. William Paley, Natural Theology (1802), chapters 1–3.