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 man who is already under sentence of excommunication cannot be excommunicated any further. For the Apostle says (i Cor. v. 12): What have I to do to judge them that are without? Now those who are excommunicated are already outside the Church.
Therefore the Church cannot exercise any further judgment on them, so as to excommunicate them again.
Obj. 2: Further, Excommunication is privation of divine things and of the communion of the faithful. But when a man has been deprived of a thing, he cannot be deprived of it again. Therefore one who is excommunicated cannot be excommunicated again.
On the contrary, Excommunication is a punishment and a healing medicine. Now punishments and medicines are repeated when necessary. Therefore excommunication can be repeated.
I answer that, A man who is under sentence of one excommunication, can be excommunicated again, either by a repetition of the same excommunication, for his greater confusion, so that he may renounce sin, or for some other cause. And then there are as many principal excommunications, as there are causes for his being excommunicated.
Reply Obj. 1: The Apostle is speaking of heathens and of other unbelievers who have no (sacramental) character, whereby they are numbered among the people of God. But since the baptismal character whereby a man is numbered among God's people, is indelible, one who is baptized always belongs to the Church in some way, so that the Church is always competent to sit in judgment on him.
Reply Obj. 2: Although privation does not receive more or less in itself, yet it can, as regards its cause. In this way an excommunication can be repeated, and a man who has been excommunicated several times is further from the Church's prayers than one who has been excommunicated only once.
Also online, linked only: the same translation at New Advent and the Latin text at Corpus Thomisticum. Neither is copied here.