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.[246] 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 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.