Passive intellect
The passive intellect (Latin: intellectus possibilis; also translated as potential intellect or material intellect), is a term used in philosophy alongside the notion of the active intellect in order to give an account of the operation of the intellect (nous), in accordance with the theory of hylomorphism, as most famously put forward by Aristotle.

Aristotle's conception 
Aristotle gives his most substantial account of the passive intellect () in De Anima (On the Soul), Book III, chapter 4. In Aristotle's philosophy of mind, the passive intellect "is what it is by becoming all things".  By this Aristotle means that the passive intellect can potentially become anything by receiving that thing's intelligible form.  The active intellect () is then required to illuminate the passive intellect to make the potential knowledge into knowledge in actuality, in the same way that light makes potential colors into actual colors. The analysis of this distinction is very brief, which has led to dispute as to what it means.

Interpretations 
Greek thought

While Greek commentators such as Alexander of Aphrodisias and Themistius were broadly silent on the active intellect (debate over this would only become heated in the thirteenth-century Christian West in the context of debates over whether Avicenna or Averroes provided the account of the working of the intellect that best cohered with Christian doctrine), they provided a great deal of commentary on the nature of the passive intellect. For instance, to Alexander of Aphrodisias (who coined for this power the term 'material intellect', a name later taken up by Averroes) the passive intellect was a separate intellect from the active.

Averroes and Aquinas

Later philosophers, including Averroes and St. Thomas Aquinas, proposed mutually exclusive interpretations of Aristotle's distinction between the active and passive intellect.  Other terms used are "material intellect" and "potential intellect", the point being that the active intellect works on the passive intellect to produce knowledge (acquired intellect), in the same way that actuality works on potentiality or form on matter.

Averroes held that the passive intellect, being analogous to unformed matter, is a single substance common to all minds, and that the differences between individual minds are rooted in their phantasms as the product of the differences in the history of their sense perceptions. Aquinas argues against this position in Disputed Questions on the Soul (Quaestiones disputatae de Anima), asserting that, while the passive intellect is one specifically, numerically it is many, as each individual person has their own passive intellect.

Passive intellect in Islamic philosophy

Passive intellect is identical with Aql Bil Quwwah in Islamic philosophy. Aql bi-al-quwwah, defined as reason, could abstract the forms of entities with which it is finally identified. For Farabi, the potential intellect becomes actual by receiving the form of matter. In other words, Aql Hayulany tries to separate the forms of existents from their matter. The form become identical with Aql. Farabi also recognised the potential intellect as part of soul.

References

Sources
 
 
Commentarium magnum in Aristotelis De anima libros, ed. Crawford, Cambridge (Mass.) 1953: Latin translation of Averroes' long commentary on the De Anima
Averroes (tr. Alain de Libera), L'intelligence et la pensée, Paris 1998: French translation of Averroes' long commentary on book 3 of the De Anima

External links
Catholic Encyclopedia article
Aquinas, ''De Unitate Intellectus Contra Averroistas (Latin)
 Aquinas, On the Unity of the Intellect, against the Averroists (English)
Barrionuevo, "La capacidad productiva del nous (DA, 3.5)" (Spanish)

Concepts in ancient Greek philosophy of mind
Aristotelianism