Probably the one notion that most comprehensively expresses the Aristotelian view is that of Taos, end. The nature of a thing is equivalent to its end, each thing is to be conceived as being, or as coming to be, in definite relations with its surroundings, and so ultimately with the whole to which it belongs. And, as member of the whole, it necessarily has some function to fulfill, and in ful filling that function it necessarily has some structure which will enable it to accomplish its end. Hence the importance of a compre hensive knowledge of the particular circumstances which attend on the exercise of its functions by anything. An exhaustive knowl edge of these particular circumstances would be essentially a knowledge of how the thing stood related to the whole of which it is a part ; and even though this cannot be attained, yet knowl edge of the particular circumstances is always of assistance in the attempt to discover a thing's essential nature.
Aristotle viewed the several forms of cognitive activity as fall ing into a kind of order or scale. The first, that which is the basis of the whole, is sense-perception which has for its objects individual things (7-a 6vra). Sense-perception was regarded by him as the faculty of receiving the forms of things apart from their matter, just as the figure of a seal is taken on by the wax without the gold or other metal of which the seal is composed.
But sense-perception was not merely a passive receptivity ; it was an act of the mind, a discriminative act. In the content of sense-perception Aristotle recognised (a) for each sense a special characteristic, as, for example, colour for the eye, sound for the ear (iSca (b) common properties which are apprehended by several of the senses, or by sense in an unspecialised way, as, for example, figure or movement (Kowa, atcrenra) and (c) what he calls "incidental" properties (alo-Orra Kara avy3e13r)c6s), as for example, that the white object seen is the son of Diares. Sense perception proper is the awareness of a sensum (an alo-Onrov) which is distinct from the act of sensing, and is a concomitant of an object (inroKeigevov). The sensum is indeed dependent upon the perceiver; it results from the meeting of a certain object and a certain percipient subject ; and if either the object or the per cipient's body undergoes change a different sensum will be pro duced. Yet the object, through the stimulation of which the act of perception arises, has a nature of its own independent of its being perceived.
The perceptive faculty operates, according to Aristotle, not only as specialised into the five senses, but in a common or unspecialised way; and the functions of the so-called senses communis are (a) to apprehend the "common sensibles" and the "incidental sensi bles," (b) to enable us to become aware that we perceive,— that is to say, to be aware of self in perceiving, and (c) to enable us to discriminate and compare the data afforded by the several senses. All creatures endowed with alo-Oriats have a
certain power of knowing, but only those that in addition pos sess the power of memory (AviLun), the power of preserving and reproducing presentations and of referring them to what has been perceived in the past, are able to advance to generalised knowledge. Memory is dependent upon imagination (cPavracia), the mechanically determined consequent of perception, which operates after the sensible object has gone, upon the relics or images that remain in the sense-organs. Through the aid of memory there is generated in the mind that kind of knowledge to which Aristotle gave the name of experience (&urEtpia), the essence of which consists in the grouping of re sembling particulars under general heads. Experience, or empirical knowledge, was distinguished from the higher forms of science and practical skill (Ertariurri and 74xPn) by the fact of its going in no way beyond the resemblance of the particulars compared. When, on the other hand, generalisations are seen to rest on a reason, then scientific insight has been attained.
A truly scientific proposition must, therefore, necessarily be uni versal, and the universality has a two-fold aspect. The proposi tion is (a) Kara ravros, it embraces a whole class in its scope; it is (b) KaO' abrO, it states the essence (Etbos) which underlies the empirically discoverable resemblances in the several members of the class. The highest stage of all is furnished by the faculty of intellect or reason (Pas), which is receptive of "intelligible form," as sense is of "sensible form." It was certainly difficult for Aris totle to exhibit his doctrine of vas in strict conformity with what he had said respecting sense-perception and scientific insight.
On the one hand, he describes it as the faculty which apprehends principles,—that is to say, truths which are not mediated by any discursive reasoning, which are immediate, and in regard to which it is not possible that there should be the alternative open to other propositions of being either true or false. First principles are directly or intuitively apprehended. On the other hand, Pas was not supposed by him to operate in abstracto. It apprehended principles in and through the matter furnished by the lower facul ties of mind. Although a thought is not an image, we cannot think without images.