Third Question: On the Mutability of Ecclesiastical Law

372. Ecclesiastical law, like every human law, can be changed, and indeed in two ways:

a) Some are causes excusing from law, which do not take away the obligation but impede it from being applied here and now to someone, and excuse from transgression of the law, namely: 1) ignorance, which impedes in the subject only formal and subjective obligation, and 2) inability, which also impedes material and objective obligation.

b) Other causes are exempting from law, which take away the obligation either in a particular case, with regard to certain persons only, so that the law itself does not cease, which happens by 3) dispensation, and 4) privilege; or in general so that the law ceases, either 5) intrinsically, by cessation of the end, or extrinsically, by 6) abrogation and derogation, and 7) custom. Concerning these things we must now speak in species.