Chapter Eight: On the Causes of the Variation Affecting the Rational Faculty Found in the Human Species

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may God spare us it

Chapter Eight

On the causes of the variation that befalls the rational power present (1) in the human species

As for the first cause, it is that the brain of man has three ventricles: the first, in which is the common sense (al-ḥiss al-mushtarak); the second, which is the dwelling of the imaginative power (al-quwwah al-mutakhayyilah); and the last, in which is the memorative power. The first must have a mixture (mizāj) that is moist with a little dryness in it, so that it may receive the form (ṣūrah) of the sensibles with ease and they may not pass away swiftly, by reason of the dryness present in it. For this reason instruction was laid down for children, so that the sciences may be firmly rooted in their inward powers by reason of the moisture that prevails in those [14] powers; for the age of old age brings an increase of dryness in those powers, so that the reception of the sciences becomes hard for them (2). As for the mixture of the middle cavity, it must incline to heat, since it is the mine of the syllogisms, and these stand in need of swiftness of motion and of heat — but on condition of balance, for excess entails the mingling of the true with the false, and deficiency entails the absence of motion. As for the last cavity, it must incline to dryness, so that it may keep what is imprinted of the intelligible forms

The second cause is that between the first ventricle and the middle one there is a passage (3) in which there is ( 16 )

a body resembling a worm. Expansion and refinement befall it, that passage opens, and the spirit (rūḥ) runs from the first to the middle; and there the forms pass over from the common (1) to the cogitative. And when that body draws together and thickens, it stops up that passage, the spirit is held back from running (2), and the passage of the forms is barred. Therefore every man whose brain’s mixture is thick, in whom the motion of the said body is hard, is on that account of little understanding and far (3) from knowledge; and he whose brain inclines to heat is the reverse of that

The third cause is the shape of the head. The best of its shapes is that which is a little compressed between the right and the left, so that there results from it something like a circle on the side of the forehead and another, smaller, on the side of the nape; for the front part is a cavity, so that if the front part is obstructed, harm accrues to the common sense; and if the cogitative (4) is obstructed, the one mentioned is harmed; and if both are obstructed, both are harmed

The fourth cause is that the head and the body are either both large, or both small, or the head small (5) and the body large, or the reverse. In the first, the brain and the heart are (6) strong, and that man is complete in

— Notes —

[15] 1 ) The word al-ḥāṣilah ought to be put in place of al-mawjūah.

[15] 2 ) In the original: ʻalayhi.

[15] 3 ) In the original: malak.

[16] 1 ) That is, “the common sense”.

[16] 2 ) Omitted in the original: al-jarayān.

[16] 3 ) By “far from knowledge” he intended “of little knowledge”.

[16] 4 ) He intends al-mufakkirah, the cogitative power.

[16] 5 ) Omitted in the original: al-raʼs ṣaghīran.

[16] 6 ) Omitted in the original: fīhi.