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 seems that a person does not incur excommunication for communicating with one who is excommunicated. For a heathen or a Jew is more separated from the Church than a person who is excommunicated. But one does not incur excommunication for communicating with a heathen or a Jew. Neither, therefore, does one for communicating with an excommunicated Christian.
Obj. 2: Further, If a man incurs excommunication for communicating with an excommunicated person, for the same reason a third would incur excommunication for communicating with him, and thus one might go on indefinitely, which would seem absurd. Therefore one does not incur excommunication for communicating with one who is excommunicated.
On the contrary, An excommunicated person is banished from communion. Therefore whoever communicates with him leaves the communion of the Church: and hence he seems to be excommunicated.
I answer that, A person may incur excommunication in two ways. First, so that the excommunication includes both himself and whosoever communicates with him: and then, without any doubt, whoever communicates with him, incurs a major excommunication. Secondly, so that the excommunication is simply pronounced on him; and then a man may communicate with him either in his crime, by counsel, help or favour, in which case again he incurs the major excommunication, or he may communicate with him in other things by speaking to him, greeting tum, or eating with him, in which case he incurs the minor excommunication.
Reply Obj. 1: The Church has no intention of correcting unbelievers as well as the faithful who are under her care: hence she does not sever those, whom she excommunicates, from the fellowship of unbelievers, as she does from the communion of the faithful over whom she exercises a certain power.
Reply Obj. 2: It is lawful to hold communion with one who has incurred a minor excommunication, so that excommunication does not pass on to a third person.
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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.