This essay explores Aristotle’s conception of the active intellect or nous poiētikos. The earliest, medieval, and most recent interpretations of this concept are discussed. It is argued that even Aristotle’s immediate disciples disagreed in their conception of the active intellect, nor was there any more unanimity in the Middle Ages. According to Trendelenburg, the difficulty of the Aristotelian doctrine lies in the fact that the nous is sometimes said to be so intimately connected with the other faculties of the soul (...) that it appears to be incapable of existing without them. When it is viewed the highest nous, as nous poiētikos, it is separated from the rest of human nature and contrasted with it as something higher and its ruler. (shrink)