what is intelligible, because intelligibles are universals encompassing this particular and that particular, whether a self-subsisting substance or a meaning inherent in a substance. Inward and outward sensation apprehend only particulars, so there is no incompatibility between the two. Outward sensation apprehends observable entities and their manifest attributes, such as colours and movements. What they called estimation, they held to apprehend meanings within sensible objects that outward sensation cannot apprehend, such as friendship, enmity, and the like. Imagination consists in representing such sensible objects inwardly.

For this reason, they divided apprehension into three kinds: sensation, imagination, and intellect.

Ibn Sīnā said:

“A thing is perceived through the senses when it is observed, and then imagined in its absence through the representation of its image inwardly. Take, for example, Zayd, whom you have seen: when he is absent from you, you imagine him. It may also be apprehended intellectually when, from Zayd, for example, one conceives the meaning of ‘human being’, which is also found in others.

“When it is perceived through the senses, it is enveloped in coverings extraneous to its essential nature. Were these removed, they would not affect the core of its essential nature. These include location, position, quality, and a particular magnitude; if