The story is far too long and the theme involved too grave and difficult for treatment here. But I would venture to suggest that Aristotle inclined to slur over the physical and lean the more to the final cause, for this simple reason (whatever other reasons there may be), that he was a better biologist than a physicist: that he lacked somewhat the mathematical turn of mind which was intrinsic to the older schools of philosophy. For better for worse the course he took, the choice he made, was of incalculable import, and had power for centuries to guide (dare we say, to bias) the teaching of the schools, the progress of learning, and the innermost beliefs of men. In this one short but pregnant chapter of Aristotle's there is far more than we can hope even to epitomize. He has much to say in it of 'classification', an important matter indeed, and he discusses it as a great logician should, in all its rigour. Many commentators have sought for Aristotle's 'classification of animals'; for my part I have never found it, and, in our sense of the word, I am certain it is not there. An unbending, unchanging classification of animals would have been something foreign to all his logic; it is all very well, it becomes practically necessary, when we have to arrange our animals on the shelves of a museum or in the arid pages of a 'systematic' catalogue; and it takes a new complexion when, or if, we can attain to a real or historical classification, following lines of actual descent and based on proven facts of historical evolution. But Aristotle (as it seems to me) neither was bound to a museum catalogue nor indulged in visions either of a complete _scala naturae_ or of an hypothetical phylogeny. He classified animals as he found them; and, as a logician, he had a dichotomy for every difference which presented itself to his mind. At one time he divided animals into those with blood and those without, at another into the air-breathers and the water-breathers; into the wild and the tame, the social and the solitary, and so on in endless ways besides. At the same time he had a quick eye for the great natural groups, such 'genera' (as he called them) as Fish or Bird, Insect or Mollusc. So it comes to pass that, while he fashioned no hard and fast scheme of classification, and would undoubtedly (I hold) have thought it vain to do so, the threads of his several partial or temporary classifications come together after all, though in a somewhat hazy pattern, yet in a very beautiful and coherent parti-coloured web. And though his order is not always our order, yet a certain exquisite orderliness is of the very essence of his thought and style. It is the characteristic which Molière hits upon in _Les Femmes savantes_,--'Je m'attache _pour l'ordre_ au péripatétisme'.