removed also. (b) Form is of two kinds, that which is the essential of the genius, being inseparable from the matter, and that which serves to describe the thing itself, i.e., the ten Aristotelian, categories—substance, quantity, quality, relation, place, time, situation, condition, action, and passion; and this form is the faculty whereby a thing (shay') is produced from formless matter, as fire is produced from the coincidence of dryness and heat, the matter being the dryness and heat, the form being the fire; without form the matter is abstract but real, becoming a thing when it takes form. As De Vaux points out (Avicenne, p. 85) this illustration shows that al-Kindi does not grasp Aristotle's meaning correctly. (c) Movement is of six kinds: two are variations in substance, as either generation or corruption, i.e., production or destruction; two are variations in quantity by increase or decrease; one is variation in quality, and one is change of position. (d) Time is itself akin to movement, but proceeds always and only in one direction; it is not movement, though akin, for movement shows diversities of direction. Time is known only in relation to a "before" or "after," like movement in a straight line and at a uniform rate, and so can only be expressed as a series of continuous numbers. (e) Place is by some supposed to be a body, but this is refuted by Aristotle: it is rather the surface which surrounds the body. When the body is taken away the place does not cease to exist, for the vacant space is instantly filled
