[9] Ibid. p. 405, a. 13, b. 19.
[10] Aristot. De Animâ, I. ii. p. 404, a. 16; p. 407, b. 27.
A peculiar theory was delivered by Xenokrates (who, having been fellow-pupil with Aristotle under Plato, afterwards conducted the Platonic School, during all the time that Aristotle taught at the Lykeium), which Aristotle declares to involve greater difficulty than any of the others. Xenokrates described the soul as “a number (a monad or indivisible unit) moving itself.�[11] He retained the self-moving property which Plato had declared to be characteristic of the soul, while he departed from Plato’s doctrine of a soul with continuous extension. He thus fell back upon the Pythagorean idea of number as the fundamental essence. Aristotle impugns, as alike untenable, both the two properties here alleged — number and self-motion. If the monad both moves and is moved (he argues), it cannot be indivisible; if it be moved, it must have position, or must be a point; but the motion of a point is a line, without any of that variety that constitutes life. How can the soul be a monad? or, if it be, what difference can exist between one soul and another, since monads cannot differ from each other except in position? How comes it that some bodies have souls and others not? and how, upon this theory, can we explain the fact that many animated bodies, both plants and animals, will remain alive after being divided, the monadic soul thus exhibiting itself as many and diverse? Besides, the monad set up by Xenokrates is hardly distinguishable from the highly attenuated body or spherical atom recognized by Demokritus as the origin or beginning of bodily motion.[12]
[11] Ibid. iv. p. 408, b. 32.
[12] Ibid. p. 409, b. 12.
These and other arguments are employed by Aristotle to refute the theory of Xenokrates. In fact, he rejects all the theories then current. After having dismissed the self-motor doctrine, he proceeds to impugn the views of those who declared the soul to be a compound of all the four elements, in order that they might account for its percipient and cognitive faculties upon the maxim then very generally admitted[13] — That like is perceived and known by like. This theory, the principal champion of which was Empedokles, appears to Aristotle inadmissible. You say (he remarks) that like knows like; how does this consist with your other doctrine, that like cannot act upon, or suffer from, like, especially as you consider that both in perception and in cognition the percipient and cognizant suffers or is acted upon?[14] Various parts of the cognizant subject, such as bone, hair, ligaments, &c., are destitute of perception and cognition; how then can we know anything about bone, hair, and ligaments, since we cannot know them by like?[15] Suppose the soul to be compounded of all the four elements; this may explain how it comes to know the four elements, themselves, but not how it comes to know all the combinations of the four; now innumerable combinations of the four are comprised among the cognita. We must assume that the soul contains in itself not merely the four elements, but also the laws or definite proportions wherein they can combine; and this is affirmed by no one.[16] Moreover, Ens is an equivocal, or at least a multivocal, term; there are Entia belonging to each of the ten Categories. Now the soul cannot include in itself all the ten, for the different Categories have no elements in common; in whichever Category you rank the soul, it will know (by virtue of likeness) the cognita belonging to that category, but it will not know the cognita belonging to the other nine.[17] Besides, even if we grant that the soul includes all the four elements, where is the cementing principle that combines all the four into one? The elements are merely matter; and what holds them together must be the really potent principle of soul; but of this no explanation is given.[18]
[13] Ibid. v. p. 409, b. 29.
[14] Aristot. De Animâ, I. v. p. 410, a. 25.
[15] Ibid. a. 30.
[16] Ibid. p. 409, b. 28; p. 410, a. 12.