The sources of the "Attributes of the Soul" are no doubt the various Neo-Platonic writings current among the Arabs in the tenth and eleventh centuries, of which we spoke in the Introduction (p. xx) and in the chapter on Gabirol (p. 63 f.). Gabirol himself can scarcely have had much influence on our author, as the distinctive doctrine of the "Fons Vitæ" is absent in our treatise. The reader will remember that matter and form, according to Gabirol, are at the basis not merely of the corporeal world, but that they constitute the essence of the spiritual world as well, the very first emanation, the Universal Intelligence, being composed of universal matter and universal form. As we shall see this is not the view of the "Attributes of the Soul." Matter here occupies the position which it has in Plotinus and in the encyclopædia of the Brethren of Purity. It is the fourth in order of emanations, and the composition of matter and form begins with the celestial sphere, which is the fifth in order. Everything that precedes matter is absolutely simple. At the same time it seems clear that he was familiar with Gabirol's doctrine of the will. For in at least two passages in the "Attributes of the Soul" (chs. 11 and 13)[134] we have the series, vegetative soul, spheral impression, [psychic power--omitted in ch. 13], universal soul, intellect, will. The "Categories" of Aristotle is also clearly evident in the "Attributes of the Soul." It is the ultimate source of the definition of accident as that which resides in substance without being a part of it, but yet in such a way that without substance it cannot exist.[135] The number of the species of motion as six[136] points in the same direction. This, however, does not prove that the author read the "Categories." He might have derived these notions, as well as the list of the ten categories, from the writings of the Brethren of Purity. The same thing applies to the statement that a spiritual substance is distinguished from a corporeal in its capacity of receiving its qualities or accidents without limits.[137] This probably goes back to the De Anima of Aristotle where a similar contrast between the senses and the reason is used as an argument for the "separate" character of the latter. The doctrine of the mean in conduct[138] comes from the ethics of Aristotle. The doctrine of the four virtues and the manner of their derivation is Platonic,[139] and so is the doctrine of reminiscence, viz., that the soul recalls the knowledge it had in its previous life.[140] Ibn Sina is one of the latest authors mentioned in our work; hence it could not have been written much before 1037, the date of Ibn Sina's death. The _terminus ad quem_ cannot be determined.