A rank (martaba) such as knowledge, which is a conditioned subtlety (mukayyad laṭīf), renders the dense (kathīf)—that is, what is thickened and perceptible—into a perceivable form. Undoubtedly, here it manifests in the form of milk. This rank, like the sensibles (maḥsūsāt), renders the conditioned dense (mukayyad kathīf)—that is, what is limitedly dense—into a subtle (laṭīf) state. Undoubtedly, here it manifests in the form of imagination (hayāl). The origin of this rank is the faculty in the first cavity of the brain.
Know that, when you take in all the forms (ṣuwar) that appear in this rank—whether from the sensibles (perceptible by the senses) or the non-sensibles (imperceptible)—and when you contemplate all the distinct forms except those defined by their very essence (as in the separation of four from three), an independent world is unveiled to you. This world, together with the faculty in the brain and the forms of imagination, is in fact the barzakh (the isthmus) between all abstract (mujarrad) and concrete (mushahhas) existents. Some Sufis have called this second rank the absolute imagination (hayāl-i muṭlaq) and the separated (munfaṣil). (Asfār, 131)