204 THE PHILOSOPHY OF BIOLOGY 



follows the methods of ancient philosophy. In 

 classical metaphysical systems mutability was an 

 illusion. Behind the confusion and change given to 

 sensation there is something that is immutable and 

 eternal. If there is change there is something that 

 changes ; or, at least there ought to be something that 

 changes when it is perceived through the mists of 

 sensation, just as the image of a well-known object 

 on the horizon wavers and is distorted by refraction. 

 This immutable reality is the Form or Essence of the 

 Platonic Idea : that which is in some way degraded 

 by its projection into materiality, so that we become 

 aware of it only through our imperfect organs of 

 sense. We do not see the Form itself, but its quality 

 rather, the Form with something added or something 

 taken away from it. 



The Form itself is only a phase in a process of 

 transmutation. Everything that exists in time flows 

 or passes into something else. But it is not a momen- 

 tary or instantaneous view of the flux that we see, 

 but rather a certain aspect of the reality that flows, that 

 in some way expresses the nature of the transmutation 

 from one Form into another. The sculptor represents 

 the motion of a man running by symbolising in one 

 attitude all the actions of body and limbs ; so that 

 from our actual, sensible experience or intuition of 

 the movement of the runner we see in the rigid marble 

 all the plasticity of life. The instantaneous photo- 

 graph shows us a momentary fixed attitude of the 

 runner — an attitude which is strange and unfamiliar. 

 The Idea does not, then, represent a moment of 

 becoming like the photograph, but rather a typical 

 or essential phase of the process of transmutation, 

 just as the sculptor represents in immobile form the 

 characteristic leap forward of the runner. Just as 



