 The power of the mind to grasp universals was traditionally attributed to what was called the “agent intellect,” the intellect as active or productive. The idea of the agent (or active) intellect is one of the most complex and contested aspects of medieval epistemology. It has its origins in some cryptic remarks made by Aristotle (DA 430a10–19), in which he distinguishes between two aspects of the mind. There is the mind as “that which becomes all things” (nous tōi panta ginesthai) and there is the mind as “that which makes all things” (ho … tōi panta poiein). Behind these descriptions is the idea that the mind “becomes” the object of its knowledge, in the sense of taking on its intelligible form without the matter in which it was originally embodied. The mind as passive—as that which becomes all things—stands in relation to the mind that makes all things in the same way that prime matter, which is pure potential, stands in relation to its shaping principle. Aristotle describes the mind as active or productive—the nous poiētikos, to use a phrase coined by his commentators—in terms that suggest something immaterial: it is “separable, unmixed, and impassible.” This may be because it is not so much a substance, as an operation or function; indeed Aristotle describes the nous poiētikos as “by nature activity” (tēi ousiai … energeia).