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Why was the Supplement added to the unfinished Summa theologiae?
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St. Thomas Aquinas
St. Thomas Aquinas, from the Demidoff Altarpiece, tempera on poplar by Carlo Crivelli, 1476; in the National Gallery, London.
The Supplement was added to the Summa theologiae because St. Thomas Aquinas left the work unfinished at the time of his death in 1274.12
Aquinas had only completed the first 90 questions of the third part of the Summa when his work was aborted. To provide a sense of completion to the systematic compendium, the Supplement was compiled in the 14th century using Aquinas’s earlier commentary on Peter Lombard’s Sentences.1