Council of Trent: Session XXIV, Reformation of Marriage, Chapter V

CHAPTER V. No one is to marry within the prohibited degrees: in what manner dispensation is to be granted therein.

If any one shall presume knowingly to contract marriage within the prohibited degrees, he shall be separated, and be without hope of obtaining a dispensation; and this shall much the rather have effect in regard of him who shall have dared not only to contract such a marriage, but also to consummate it. But if he have done this in ignorance, but yet has neglected the solemnities required in contracting matrimony, he shall be subjected to the same penalties. For he who has rashly despised the wholesome precepts of the Church, is not worthy to experience without difficulty her bounty. But if, having observed those solemnities, some secret impediment be afterwards discovered, of which it was not unlikely that he should be ignorant, he may in this case more easily obtain a dispensation, and that gratuitously. As regards marriages to be contracted, either no dispensation at all shall be granted, or rarely, and then for a cause, and gratuitously. A dispensation shall never be granted in the second degree, except between great princes, and for a public cause.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).