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 neither are they bound to pay the debt at a festal time. For those who commit a sin as well as those who consent thereto are equally punished (Rom. i. 32). But the one who pays the debt consents with the one that asks, who sins. Therefore he sins also.
Obj. 2: Further, It is an affirmative precept that binds us to pray, and therefore we are bound to do so at a fixed time. Therefore one ought not to pay the debt at a time when one is bound to pray, as neither ought one at a time when one is bound to fulfil a special duty towards a temporal master.
On the contrary, It is written (i Cor. vii. 5): Defraud not one another, except by consent, for a time, etc. Therefore when one spouse asks the other must pay.
I answer that, Since the wife has power of her husband's body, and vice versa, with regard to the act of procreation, the one is bound to pay the debt to the other, at any season or hour, with due regard to the decorum required in such matters, for this must not be done at once openly.
Reply Obj. 1: As far as he is concerned he does not consent, but grants unwillingly and with grief that which is exacted of him; and consequently he does not sin. For it is ordained by God, on account of the weakness of the flesh, that the debt must always be paid to the one who asks lest he be afforded an occasion of sin.
Reply Obj. 2: No hour is fixed for praying, but that compensation can be made at some other hour; wherefore the argument is not cogent.
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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.