From the Supplement, compiled after Aquinas’s death from his Commentary on the Sentences and transcribed here from the 1917 to 1922 printings. About the Supplement.
Text: Summa Theologiae, Supplement to the Third Part (Supplementum Tertiae Partis), transcribed from Internet Archive scans, translated by the Fathers of the English Dominican Province. The Supplement, compiled after Aquinas’s death from his earlier Commentary on the Sentences, in the same English Dominican translation as the Gutenberg Parts. Transcribed by Bibliotheca Catholica from the OCR of four Internet Archive scans of the pre-1931 printings (Questions 1 to 33 from the 1917 Washbourne and Benziger volume, 34 to 68 from the 1922 volume, 69 to 86 from the 1921 volume, and 87 to 99 from the 1922 Benziger volume), with OCR errors corrected and doubtful passages marked, not rewritten. 99 questions and 446 articles. The two appendices printed after Question 99 are not included. Sources, SHA-256 of each OCR file, and the method are in the source record. Rights: Public domain (US)
The Supplement is not a Project Gutenberg text. It is Bibliotheca Catholica’s transcription of public-domain scans at the Internet Archive; obvious OCR errors were corrected, and passages marked “OCR uncertain” could not be confidently corrected, so check them against the linked scan page.
Objection 1: It would seem that it is a mortal sin to ask for the debt at a holy time. For Gregory says (Dial, i.) that the devil took possession of a woman who had intercourse with her husband at night and came in the morning to the procession. But this would not have happened had she not sinned mortally. Therefore, etc.
Obj. 2: Further, Whoever disobeys a Divine command commits a mortal sin. Now the Lord commanded (Exod. xix. 15): Come not near your wives, when namely they were about to receive the Law. Much more therefore do husbands sin mortally if they have intercourse with their wives at a time when they should be intent on the sacred observances of the New Law.
On the contrary, No circumstance aggravates infinitely. But undue time is a circumstance. Therefore it does not aggravate a sin infinitely, so as to make mortal what was otherwise venial.
I answer that, To ask for the debt on a feast day is not a circumstance drawing a sin into another species; wherefore it cannot aggravate infinitely. Consequently a wife or husband does not sin mortally by asking for the debt on a feast day. It is however a more grievous sin to ask for the sake of mere pleasure, than through fear of the weakness of the flesh.
Reply Obj. 1: This woman was punished not because she paid the debt, but because afterwards she rashly intruded into the divine service against her conscience.
Reply Obj. 2: The authority quoted shows not that it is a mortal sin but that it is unbecoming. For under the Old Law which was given to a carnal people many things were required under an obligation of precept, for the sake of bodily cleanness, which are not required in the New Law which is the law of the spirit.
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Also online, linked only: the same translation at New Advent and the Latin text at Corpus Thomisticum. Neither is copied here.