A key is useful only in that lock for which it was designed.

A key is useful only in that lock for which it was designed. Persons who have a compound personality speak in more than one language. One who is both poet and philosopher speaks in the languages of poetry and philosophy, which remain separate.

For example, compare how and in what language Avicenna discussed spirit, body, and the relation between them in his books of philosophy (such as the Shifa' and the Isharat ) on the one hand and in his famous “'Ayniyya” qasida on the other, whose opening line is “It descended to you from the highest locus, [And grew] filled with pride and refusal.” We must distinguish the languages of science and philosophy from the languages of poetry and the pulpit so that we do not, like so many atheists and materialists, become faced with grave and unpardonable errors.

In fact, philosophers have theories that correspond with what appears in the language of poetry. For instance, Plato holds that the spirit is an eternal substance preexistent to the body. When the body is ready, the spirit “descends” from its level and is “attached” to the body.

This theory is totally dualistic in that it regards spirit and body as two separate and disjoined substances and sees their relation as something accidental and nominal, like the relation of bird and nest or of rider and mount. It recognises no substantial and natural connection representing a kind of unity and essential connection between them. But before long, Plato's student, Aristotle, demolished this theory.

Aristotle noted that Plato and his predecessors had focused on the aspect of duality and contrast between spiritual phenomena and physical phenomena but ignored their unity and interdependence. Aristotle noted that one cannot regard the interrelation and interdependence of spirit and body as superficial, like that of bird and nest or that of rider and mount, but that the relation of spirit and body is certainly more profound and natural.

Aristotle regarded the relation of spirit and body as belonging to the species of relation of the form to the matter in which it originates, with the difference that, because the rational faculty is abstract, it is a form with matter, not a form in matter. The idea that the spirit is an eternal substance in actu does not persist into Aristotle's philosophy. The spirit is not eternal; it is created in time. At first it is purely potential.

It acquires no sort of prior knowledge; it actualises all its knowledge in this world.