CHAPTER I

INTRODUCTORY. THE IMPORTANCE AND DIFFICULTY OF THE STUDY OF THE SOUL

             HOLDING as we do that knowledge is a good and honourable thing, yet that some kinds of knowledge are more so than others, either because they are more certain or because they deal with subjects more excellent and wonderful, we naturally give a primary place, for both these reasons, to an enquiry about the soul.§§ 1-6

             Indeed an acquaintance with the soul would seem to help much in acquiring all truth, especially about the natural world; for it is, as it were, the principle of living things.§ 7

             We seek then to consider and understand, first, its nature and essence, then whatever qualities belong to it. Of these, some seem to be proper to the soul alone, others to be shared in common and to exist in animate beings on account of it.§ 8

             To ascertain, however, anything reliable about it is one of the most difficult of undertakings. Such an enquiry being common to many topics--I mean, an enquiry into the essence, and what each thing is--it might seem to some that one definite procedure were available for all things of which we wished to know the essence; as there is demonstration for the accidental properties of things. So we should have to discover what is this one method. But if there is no one method for determining what an essence is, our enquiry becomes decidedly more difficult, and we shall have to find a procedure for each case in particular. If, on the other hand, it is clear that either demonstration, or division, or some such process is to be employed, there are still many queries and uncertainties to which answers must be found. For the principles in different subject-matters are different, for instance in the case of numbers and surfaces. Perhaps the first thing needed is to divide off the genus of the subject and to say what sort of thing it is,--I mean, whether it be a particular thing or substance, or a quality, or quantity, or any other of the different categories. Further, whether it is among things in potency or is an actuality--no insignificant distinction. Again, whether it is divisible or indivisible, and whether every soul is of the same sort or no: and if not, whether they differ specifically or generically. Indeed those who at present talk of and discuss the soul seem to deal only with the human soul. One must be careful not to leave unexplored the question whether there is a single definition of it, as of 'animal' in general, or a different one for each [of its kinds]: as, say, for horse, dog, man or god. Now 'animal' as a universal is nothing real, or is secondary; and we must say the same of any other general predicate.§§ 9-13

             Further, if there are not many souls, but only many parts of a single one, we must ask whether one ought to look first at the whole or the parts. It is difficult to see what parts are by nature diverse from one another, and whether one ought to look first at the parts or their functions, for instance at the act of understanding or at the intellective power, at the act of sensing or at the sensitive faculty; and likewise in other instances. But if one is to examine first the operations, it might be asked whether one should not first enquire about their objects, as, in the sensitive function, the thing sensed; and in the intellectual, the thing intelligible.§ 14

             Now, it seems that not only does knowledge of the essence help one to understand the causes of the accidents of any substance (as in Mathematics to know what is the straight and the curved and what is a line and what a plane enables one to discover the number of right angles to which those of a triangle are equal) but, conversely, accidental qualities contribute much to knowing what a thing essentially is. When we can give an account of such qualities (some or all) according to appearances, then we shall have material for dealing as well as possible with the essence. The principle of every demonstration is what a thing is. Hence, whatsoever definitions do not afford us a knowledge of accidents, or even a fair conjecture about them, are obviously vain and sophistical.§ 15