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 162 L. T. HOBHOUSE : detachment from others, this seems an adequate expression of the goal of knowledge. But here, secondly, we come 011 the limits of the Aristotelian conception. For Universals do not live side by side and develop themselves indepen- dently. Far the greater part of science is taken up with their correlation, the constructions they form, the ways in which they interact. And the essence itself does not show a tenth part of its nature, does not display the properties which we derive from it apart from its intercourse with the wider world. The so-called properties of the thing are mainly reactions to solicitation from other things. They must be taken into account in forming our conception of the essence, but they are not referable to it alone. We speak for instance of the properties of light or heat as following from the essential character of those phenomena. But almost any property we could name depends on other physical facts as well. Thus the ' latency ' of heat may be taken as a property dependent on the nature of heat as a mode of motion. So it certainly is. But it is equally de- pendent on the constitution of solids, liquids and gases, and might fairly be taken as a property of the physical constitu- tion of bodies. But let us take Aristotle's own favourite instance of the property of triangles that their angles are equal to two right angles. Euclid's proof of this and I suppose that it was the same proof that Aristotle had before him does not attempt to deduce it from the definition of the triangle as such. It proceeds by a special construction, the production of a side and the drawing of a line parallel to another side. In short it is based on the relation of the triangle to other lines in space, and on the properties of parallel straight lines in particular. It may be said that this only affects the method of proof and not the result. But surely an ideal systematisation of knowledge, though it might abstract from the path of discovery, would have in some way or other to exhibit the grounds of certainty. I conclude then that the conception of essence stands in an interesting relation to that of the organic universal. Under the abstract concept all the constituent elements may be regarded as essential and as equally essential, but the essence as a whole becomes identical with the concept itself. Among the elements the only possible distinction is one of value. And as this may vary according to our point of view any element may become essential or un- essential as the case may be. But under the organic universal the generic essence is necessarily the identical element as distinct from the modifications which it receives.