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 those who are of illegitimate birth should not be debarred from receiving Orders. For the son should not bear the iniquity of the father (Ezech. xviii. 20); and yet he would if this were an impediment to his receiving Orders. Therefore, etc.
Obj. 2: Further, One's own fault is a greater impediment than the fault of another. Now unlawful intercourse does not always debar a man from receiving Orders. Therefore neither should he be debarred by the unlawful intercourse of his father.
On the contrary, It is written (Deut. xxiii. 2): A mainzer, that is to say, one born of a prostitute, shall not enter into the Church of the Lord until the tenth generation. Much less therefore should he be ordained.
I answer that, Those who are ordained are placed in a position of dignity over others. Hence by a kind of propriety it is requisite that they should be without reproach, not for the validity but for the lawfulness of the sacrament, namely that they should be of good repute, bedecked with a virtuous life, and not publicly penitent. And since a man's good name is bedimmed by a sinful origin, therefore those also who are born of an unlawful union are debarred from receiving Orders, unless they receive a dispensation; and this is the more difficult to obtain, according as their origin is more discreditable.
Reply Obj. 1: Irregularity is not a punishment due for sin. Hence it is clear that those who are of illegitimate birth do not bear the iniquity of their father through being irregular.
Reply Obj. 2: What a man does by his own act can be removed by repentance and by a contrary act; not so the things which are from nature. Hence the comparison fails between sinful act and sinful origin.
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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.