distinguishes non-rational from rational potentialities (e.g. the capacity to heat and the capacity to play the flute, respectively), pointing out that the latter require desire or deliberate choice for their actualization. Because of this style of reasoning, Aristotle is often referred to as having a teleology, and sometimes as having a theory of forms. While actuality is linked by Aristotle to his concept of a formal cause, potentiality (or potency) on the other hand, is linked by Aristotle to his concepts of hylomorphic matter and material cause. Aristotle wrote for example that "matter exists potentially, because it may attain to the form; but when it exists actually, it is then in the form". Teleology is a crucial concept throughout Aristotle's philosophy. This means that as well as its central role in his physics and metaphysics, the potentiality-actuality distinction has a significant influence on other areas of Aristotle's thought such as his ethics, biology and psychology. The active intellect The active intellect was a concept Aristotle described that requires an understanding of the actuality-potentiality dichotomy. Aristotle described this in his De Anima (book 3, ch. 5, 430a10-25) and covered similar ground in his Metaphysics (book 12, ch.7-10). The following is from the De Anima, translated by Joe Sachs, with some parenthetic notes about the Greek. The passage tries to explain "how the human intellect passes from its original state, in which it does not think, to a subsequent state, in which it does." He inferred that the / distinction must also exist in the soul itself: ...since in nature one thing is the material [hulē] for each kind [genos] (this is what is in potency all the particular things of that kind) but it is something else that is the causal and productive thing by which all of them are formed, as is the case with an art in relation to its material, it is necessary in the soul [psuchē] too that these distinct aspects be present; the one sort is intellect [nous] by becoming all things, the other sort by forming all things, in the way an active condition [hexis] like light too makes the colors that are in potency be at work as colors []. This sort of intellect is separate, as well as being without attributes and unmixed, since it is by its thinghood a being-at-work, for what acts is always distinguished in stature above what is acted