definitions, that all knowledge is of something really existing, and that nothing really exists but individual things. Nevertheless, against these we have to set equally strong declarations to the effect that knowledge is of something general, not of the perishing individuals which may pass out of existence at any moment. The truth is, that we are here, as Zeller has shown,' in presence of an insoluble contradiction, and we must try to explain, not how Aristotle reconciled it with itself, for that was impossible, but how he reconciled himself to it.

His analysis of individuality was the first step in this direction. We have seen that he treats definition as a process of gradual specification, beginning with the most general notions, and working down by successive differentiations to the most particular. Now, the completed conception is itself the integration of all these differences, the bond of union holding them together. Turning to an antithetical order of ideas, to the material substance of which bodies are composed, and its various transformations, we find him working out the same vein of thought. According to the Aristotelian chemistry, an ultimate indeterminate unknowable something clothes itself with one or other of the opposing attributes, dry and moist, hot and cold; and when two of these are combined, manifests itself to our senses as one of the four elements. The elements combine in a particular manner to form homogeneous animal tissues, and these again are united into heterogeneous organs, which together constitute the living body. Here, then, we have two analogous series of specifications-one conceptual and leading down from the abstract to the concrete, the other physical, and leading up from the vague, the simple, and the homogeneous, to the definite, the complex, and the heterogeneous. Aristotle embraces both processes under a single comprehensive generalisation. He describes each of them as the continuous conversion of a

Zeller, Phil. d. Gr., II., b, 309.

possibility into an actuality. For the sake of greater clearness, let us take the liberty of substituting modern scientific terms for his cumbrous and obsolete classifications. We shall then say that the general notion, living thing, contains under it the two less general notions-plant and animal. If we only know of any given object that it has life, there is implied the possibility of its being either the one or the other, but not both together. On determining it to be (say) an animal, we actualise one of the possibilities. But the actualisation is only relative, and immediately becomes the possibility of being either a vertebrate or an invertebrate animal. The actuality vertebrate becomes the possibility of viviparous or oviparous, and so on through successive differentiations until we come (say) to a man. Now let us begin at the material end. Here are a mass of molecules, which, in their actual state are only carbon, nitrogen, and so forth. But they are potential starch, gluten, water, or any other article of food that might be named; for under favourable conditions they will combine to form it. Once actualised as such, they are possible blood-cells; these are possible tissues; these, again, possible organs, and lastly we come to the consensus of vital functions, which is a man. What the raw material is to the finished product, that are the parts to the entire organism, the elements to the compound, the genus to the species, and such in its very widest sense is potency to realisation, δύναμις to ἐντελέχεια, throughout the universe of growth and decay.1

It will be observed that, so far, this famous theory does not add one single jot to our knowledge. Under the guise of an explanation, it is a description of the very facts needing to be explained. We did not want an Aristotle to tell us that before a thing exists it must be possible. We want to know how it is possible, what are the real conditions of its existence, and why they combine at a particular moment to

1 For the general theory of Actuality and Possibility, see Metaph., VIII.

produce it. The Atomists showed in what direction the solution should be sought, and all subsequent progress has been due to a development of their method. Future ages will perhaps consider our own continued distinction between force and motion as a survival of the Peripatetic philosophy. Just as sensible aggregates of matter arise not out of potential matter, but out of matter in an extremely fine state of diffusion, so also sensible motion will be universally traced back, not to potential motion, which is all that force means, but to molecular or ethereal vibrations, like those known to constitute heat and light.

We have said, in comparing him with his predecessors, that the Stagirite unrolled Greek thought from a solid into a continuous surface. We have now to add that he gave his surface the false appearance of a solid by the use of shadows, and of aërial perspective. In other words, he made the indication of his own ignorance and confusion do duty for depth and distance. For to say that a thing is developed out of its possibility, merely means that it is developed out of something, the nature of which we do not know. And to speak about such possibilities as imperfect existences, or matter, or whatever else Aristotle may be pleased to call them, is simply constructing the universe, not out of our ideas, but out of our absolute want of ideas.

We have seen how, for the antithesis between Form and Matter, was substituted the wider antithesis between Actuality and Possibility. Even in this latter the opposition is more apparent than real. A permanent possibility is only intelligible through the idea of its realisation, and sooner or later is certain to be realised. Aristotle still further bridges over the interval between them by a new conception-that of motion. Motion, he tells us, is the process of realisation, the transformation of power into act. Nearly the whole of his Physics is occupied with an enquiry into its nature and origin. As first conceived, it is equivalent to what we call change rather than

These are, as we

to mechanical movement. The table of categories supplies an exhaustive enumeration of its varieties. have already mentioned, alteration of quality or transformation, increase or decrease of quantity, equivalent to growth and decay, and transport from place to place. Sometimes a fourth variety is added, derived from the first category, substance. He calls it generation and destruction, the coming into existence or passing out of it again. A careful analysis shows that motion in space is the primordial change on which all others depend for their accomplishment. To account for it is the most vitally important problem in philosophy.

III.

Before entering on the chain of reasoning which led Aristotle to postulate the existence of a personal First Cause, we must explain the difference between his scientific standpoint, and that which is now accepted by all educated minds. To him the eternity not only of Matter, but also of what he called Form,-that is to say, the collection of attributes giving definiteness to natural aggregates, more especially those known as organic species-was an axiomatic certainty. Every type, capable of self-propagation, that could exist at ail, had existed, and would continue to exist for ever. For this, no explanation beyond the generative power of Nature was required. But when he had to account for the machinery by which the perpetual alternation of birth and death below, and the changeless revolutions of the celestial spheres above the moon were preserved, difficulties arose. He had reduced every other change to transport through space; and with regard to this his conceptions were entirely mistaken. believed that moving matter tended to stop unless it was sustained by some external force; and whatever their advantages over him in other respects, we cannot say that the Atomists were in a position to correct him here: for their

He

theory, that every particle of matter gravitated downward through infinite space, was quite incompatible with the latest astronomical discoveries. Aristotle triumphantly showed that the tendency of heavy bodies was not to move indefinitely downwards in parallel lines, but to move in converging lines to the centre of the earth, which he, in common with most Greek astronomers, supposed to be also the centre of the universe; and seeing light bodies move up, he credited them with an equal and opposite tendency to the circumference of the universe, which, like Parmenides and Plato, he believed to be of finite extent. Thus each kind of matter has its appropriate place, motion to which ends in rest, while motion away from it, being constrained, cannot last. Accordingly, the constant periodicity of terrestrial phenomena necessitates as constant a transformation of dry and wet, and of hot and cold bodies into one another. This is explained with perfect accuracy by the diurnal and annual revolutions of the sun. Here, however, we are introduced to a new kind of motion, which, instead of being rectilinear and finite, is circular and eternal. To account for it, Aristotle assumes a fifth element entirely different in character from the four terrestrial elements. Unlike them, it is absolutely simple, and has a correspondingly simple mode of motion, which, as our philosopher erroneously supposes, can be no other than circular rotation.

Out of this eternal unchanging divine substance, which he calls aether, are formed the heavenly bodies and the transparent spheres containing them. But there is something beyond it of an even higher and purer nature. Aristotle proves, with great subtlety, from his fundamental assumptions, that the movement of an extended substance cannot be selfcaused. He also proves that motion must be absolutely continuous and without a beginning. We have, therefore, no choice but to accept the existence of an unextended, immaterial, eternal, and infinite Power on which the whole cosmos depends.