Pohle-Preuss: Impediments to forming a valid marriage

According to Pohle-Preuss:

In this chapter we propose to show, (i) that the Church possesses control over Christian marriage; (2) that this control is based on a positive divine law and can be exercised independently of the secular power; (3) that the Church has the exclusive right to establish diriment impediments.

b) In order to understand how the Church can invalidate the Sacrament of Matrimony without changing its matter and form, we must consider that the validity of the Sacrament is conditioned by the validity of the matrimonial contract. By nullifying the contract, the Church deprives the Sacrament of its basis. The validity of the contract does not depend solely on the free will of the contracting parties; it depends also on the will of God, which may manifest itself in a threefold manner : through the law of nature, through a positive law, or through an ecclesiastical precept. Hence there are three distinct classes of diriment impediments:

(1) Impediments flowing from the law of nature (e. g. impotency, error, violence);

(2) Impediments set up by a positive 'divine law (e. g. the bond of an existing marriage);

(3) Impediments established by ecclesiastical law (e. g. clandestinity, difference of religion, affinity).

....

All other impediments are of purely ecclesiastical institution, and it needs no argument to prove that the Church can dispense from laws of her own making.