Book excerpt: No Aristotelian doctrine had a greater influence on medieval philosophy and theology than that of the agent, or active, intellect. This influence, however, was mediated by a long tradition of exegesis in which the Greek commentaries of later antiquity played a dominant role. The two commentaries presented here were known to have been influential in the Middle Ages and the Renaissance. The first is a short treatise called the "De intellectu", attributed to Alexander of Aphrodisias; the second a paraphrase of Aristotle's "De anima" (3.4-8) by Themistius, which also includes a major interpretation of "De anima" (3.5), the chapte on the active intellect.