INTRODUCTION. iii 



in the work of the best sculptor.* But the presence of these will not 

 prevent you from believing that writer and sculptor worked with a pre- 

 conceived intention and for a definite end. 



So began, and so was carried on, that venerable strife, which ever 

 since has divided thinking men into two factions, and which still, though 

 twenty centuries have passed away, is fought with unchanged weapons, 

 and with increasing bitterness, and in which neither side has ever suc- 

 ceeded in reducing an opponent to submission, while each has never 

 failed to claim complete victory. 



Between these two opposite views Aristotle had now to decide. He 

 had already in his Historia Animalium set forth the i^henomena o f 

 anima l life. He had now to consider to what cause or causes these 

 phenomena were attributable. Were they due to mere necessity, or to 

 the action of intelligent foresight, or at any rate of some principle that 

 acted as intelligent foresight would do ? To neither, he says, exclu- 

 sively, but to both, though in very unequal degrees. The motions of 

 the heavenly bodies are governed by necessity, and by necessity alone. 

 But in the works of Nature, that is in the phenomena of terrestrial life, 

 this necessity is a comparatively unimportant factor. Most is the out- 

 come of design. Still some part, though but a small one, is the result 

 of necessity. There is indeed one sense in which everything in the 

 animal body may be said to be the result of necessity. When a man 

 builds a house, he must, in order to realise his plan, of necessity have 

 walls, roof, and the like. To have these he must first have bricks, 

 stones, mortar, and what not ; and, again, to furnish these, clay, lime, 

 and the other necessary materials must be previously forthcoming. So 

 is it with the animal body. The design of Nature cannot be carried 

 out without the necessary antecedents.^ In this sense then all the parts 

 of the body, and all the successive stages by which they are developed 

 one after the other, may be said to be the result jof necessity; for all 

 must necessarily be there, if the plan of Nature is to be realised. 



This "hypothetical or conditional necessity" is, however, clearly not 

 what is meant by Democritus and the Materialists when they say that 

 all organisms are the result of necessity. They speak of absolute, not I 

 of hypothetical necessity. They mean, that is to say, that organisms 

 are evolved as necessary consequences of the inherent properties of 

 matter ; not merely that the existence of the organism implies the 

 pre-existence of the necessary conditions for its production ; in short, 

 that the antecedents determine the end, and not the end the antece- 

 dents. Is this, asks Aristotle, in any degree true 7 In some measure, 

 he answers, it is ; but that measure, as already said, is but a small one. 



1 Phys. ii. 8, II. * D. P. i. i, I2. 



