In Aristotle’s De anima 3.5, the relation between intellect and thought, and between thought and object, is not accessible to discursive or conscious thought; an understanding of the relation requires nous, intuitive or “unconscious” thought. The “active” intellect is accessible to discursive reason only sporadically. “Mind does not think intermittently” (De anima 430a10–25): mind is always thinking, consciously and unconsciously. Alexander of Aphrodisias saw the active intellect as transcendent in relation to the material intellect. The thought which is an object of thought is immaterial, or unconscious. In his De intellectu (108), there must be something at work in thought for which “what it is to be intellect does not lie in its being thought by us,” that is, unconscious. In the De anima of Themistius, mind as passive, in its material potentiality, is destructible and subject to time, but mind as active is free from its material conditions. Discursive thinking is equivalent to thinking in time; time is not present in the same way in unconscious thought or dreams.In the De intellectu of Alfarabi, when intellect “thinks that existent thing which is an intellect in actuality, it does not think an existing thing outside of itself but it only thinks itself,” in unconscious thought. Intellect as the object of its own thought is inaccessible to conscious reason. Intellect ascends from material to agent intellect and we ascend “from that which is best known to us to that which is unknown,” in the unconscious. The knowledge of things which are most accessible to intellect is the lowest form of knowledge; in order to develop, intellect must come to grasp the knowledge which is least accessible and most unconscious. In the Liber Naturalis of Avicenna, intellect is seen as a palimpsest of traces of forms and thoughts of varying clarity in relation to cognition, conscious thought. Unconscious thought is seen as the intelligible in cognition in the Aristotelian model, only accessible to conscious thought or actual intellect to varying degrees. The active intellect of Averroes can be seen as a form of unconscious thought. In his Long Commentary on the De anima, the activity of the active intellect makes images intelligible in unconscious thought, according to Franz Brentano.
Hendrix, John S., "Unconscious Thought in Peripatetic Philosophy" (2014). School of Architecture, Art, and Historic Preservation Faculty Publications. 34.