176 THE MECHANISM OF LIFE 



give rise to a perception, or it may not do so; and (2) that physical 

 stimuli of different intensities may give rise to the same per- 

 ception. And therefore, when we attempt to relate our own 

 feelings with the physical stimuli which, we believe, " cause " 

 them, we do not find physical determinism. 



Perception. 



Here we must explain what we mean by " perception." The 

 term has a very great number of shades of precise meaning in 

 psychology and philosophy, and we cannot attempt to discuss 

 these, or even to choose from them. Quite arbitrarily, then, we 

 mean by perception the effect in behaviour of the body, or in 

 consciousness, that follows sensation. 



We take the affection of consciousness first in order to clear 

 the way and render our discussion quite simple. The effect of 

 a knock at the door may be nil (when we are absorbed in other 

 work and do not hear it), or it may be that we do hear it. The 

 sensation that is, the train of physical events that we have noted 

 above is the same in both cases, but in the latter -case there is 

 perception : we recognise something outside ourselves. Or in walk- 

 ing along a street we recognise a friend, when there is perception ; 

 or we fail to do so if we are " absent-minded." Yet we may be 

 quite sure that an image of the friend was formed on our retinas. 



The Objective and the Subjective. In perception, as thus 

 illustrated, there is a " sensible object " the man who knocked 

 at the door, or the knock at the door, or the knocker, or the 

 man whom we recognised in the street. A modern, scientific, 

 realistic philosopher would say that there were certainly sensible 

 objects which stimulated our organs of sense, and there were also 

 " representations," or mental images, of those sensible objects in 

 our consciousness, the sensible, external things which originate 

 physical stimuli being " objective " to us, while the images, or 

 mental representations, were " subjective." A strict idealist (for 

 there are many kinds of idealism) would say that it was quite 

 improper to speak of an external, sensible object, and that all 

 that we could be sure about was the change in our consciousness. 

 Really he ought not to explain anything of the kind to us, for all 

 that he ought to be sure about would be his state of conscious- 

 ness, we being only affections of that and having no existence 

 except in his mind. No philosopher goes that length, and yet it 

 is the logical outcome of idealism ! 



