The active intellect (Latin: intellectus agens; also translated as agent intellect, active intelligence, active reason, or productive intellect) is a concept in classical and medieval philosophy. The term refers to the formal (morphe) aspect of the intellect (nous), in accordance with the theory of hylomorphism.
The nature of the active intellect was the subject of intense discussion in medieval philosophy, as various Muslim, Jewish and Christian thinkers sought to reconcile their commitment to Aristotle's account of the body and soul to their own theological commitments. At stake in particular was in what way Aristotle's account of an incorporeal soul might contribute to understanding of the nature of eternal life.
The idea is first encountered in Aristotle's De Anima, Book III. Following is the translation of one of those passages (De Anima, Bk. III, ch. 5, 430a10-25) by Joe Sachs, with some notes about the Greek:
...since in nature one thing is the material (hylē) 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 (psychē) 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 (to phōs poiei ta dynamēi onta chrōmata energeiai chrōmata).
This sort of intellect [which is like light in the way it makes potential things work as what they are] 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 upon, as a governing source is above the material it works on.
Knowledge (epistēmē), in its being-at-work, is the same as the thing it knows, and while knowledge in potency comes first in time in any one knower, in the whole of things it does not take precedence even in time.
This does not mean that at one time it thinks but at another time it does not think, but when separated it is just exactly what it is, and this alone is deathless and everlasting (though we have no memory, because this sort of intellect is not acted upon, while the sort that is acted upon is destructible), and without this nothing thinks.
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 energeia/dynamis distinction must also exist in the soul itself. Aristotle says that the passive intellect receives the intelligible forms of things, but that the active intellect is required to make the potential knowledge into actual knowledge, in the same way that light makes potential colors into actual colors.
The passage is often read together with Metaphysics, Book XII, ch.7-10, where Aristotle also discusses the human mind and distinguishes between the active and passive intellects. In that passage Aristotle appears to equate the active intellect with the "unmoved mover" and God.[non-primary source needed]
Sachs comments that the nature of the active intellect was "the source of a massive amount of commentary and of fierce disagreement"; elsewhere, chapter 5 of De Anima has been referred to as "the most intensely studied sentences in the history of philosophy". As Davidson remarks:
Just what Aristotle meant by potential intellect and active intellect - terms not even explicit in the De anima and at best implied - and just how he understood the interaction between them remains moot. Students of the history of philosophy continue to debate Aristotle's intent, particularly the question whether he considered the active intellect to be an aspect of the human soul or an entity existing independently of man.
The early Greek commentators on Aristotle, in particular Alexander of Aphrodisias and Themistius, gave several different interpretations of the distinction between the active and passive intellects. Some of them regarded the active intellect as a power external to the human mind, Alexander going so far as to identify it with God.
Later, both these interpretations, Neoplatonist ones, and perhaps others, influenced the development of an important Arabic philosophical literature, using the term 'aql as the translation for nous. This literature was later translated into, and commented upon, in Latin and Hebrew.
Jewish and Islamic
Al-Farabi and Avicenna, and also the Jewish philosopher Maimonides, agreed with the "external" interpretation of active intellect, and held that the active intellect was the lowest of the ten emanations descending through the celestial spheres. Maimonides cited it in his definition of prophecy where
Prophecy is, in truth and reality, an emanation sent forth by the Divine Being through the medium of the Active Intellect, in the first instance to man's rational faculty, and then to his imaginative faculty.
The reason of the Islamic and Jewish Aristotelians for positing a single external Agent Intellect is that all (rational) human beings are considered by Aristotelians to possess or have access to a fixed and stable set of concepts, a unified correct knowledge of the universe. The only way that all human minds could possess the same correct knowledge is if they all had access to some central knowledge store, as terminals might have access to a mainframe computer (Kraemer 2003). This mainframe is the Agent Intellect, the "mind" of the universe, which makes all other cognition possible.
In medieval and Renaissance Europe some thinkers, such as Siger of Brabant, adopted the interpretation of Averroes on every point, as did the later school of "Paduan Averroists". Thomas Aquinas elaborated on Aristotle's distinction between the active intellect and passive intellect in his Disputed Questions on the Soul and his commentary on Aristotle's De anima, arguing, against Averroes, that the active intellect is part of the individual human personality. In his Summa Theologica, Aquinas states that "according to the teaching of our Faith, this separated intellect is God Himself, who is the creator of the soul and in whom alone the soul is beatified." Citing Gregory of Nyssa, he said "man has intellective understanding along with the angels" which are called 'minds' and 'intellects' because they have no other power than the intellective power and the will (Question 79, article 1).
A third school, of "Alexandrists", rejected the argument linking the active intellect to the immortality of the soul, while hastening to add that they still believed in immortality as a matter of religious faith. (See Pietro Pomponazzi; Cesare Cremonini.)
The active intellect, in the sense described, is more properly called the Agent Intellect, as it is the force triggering intellection in the human mind and causing thoughts to pass from the potential to the actual. It must not be confused with the "intellect in act", which is the result of that triggering, and is more akin to the psychological term "active knowledge". Another term for the final result of intellection, that is to say a person's accumulated knowledge, is the "acquired intellect". Angels are called 'minds' and 'intellects' because they have no other power than the intellective power and the will.