376 POPULAR SCIENCE MONTHLY. 



of those processes obtaining clear recognition in consciousness at 

 any one time : the remainder affect the clearest portion more or 

 less, "but exist themselves only dimly in the marginal region to 

 which I am not attending. Again, we must not suppose that in 

 ascribing to the mental state active properties we mean to imply 

 that the mental states could exist or manifest those properties 

 apart from the physical processes which form their basis, or that 

 they can act upon them in any way from outside, as the older 

 psychology supposed. I do not think, as most psychologists do, 

 that this notion is inconsistent with the doctrine of parallelism, 

 but it certainly can not be derived from it, or from the facts upon 

 which it rests. Guarding against these two errors, then, we may 

 justly regard the mental state as an active, dynamic thing, subject 

 to laws and possessed of properties into which it is the business of 

 the psychologist to inquire. 



We all know the difference between red as seen and red as we 

 think it, although the difference is hard to describe. In most per- 

 sons the sensation red is peculiarly intense and vivid, while the 

 idea is lacking in some indescribable way in both these traits. 

 Now, we have reason to believe that both mental states are of the 

 same general kind, and that the idea is capable of passing into a 

 state indistinguishable from the sensation. Such a transition is 

 known as development. In some persons certain ideas are nor- 

 mally already developed, so to speak, to their maximum degree. 

 A friend of mine tells me that, so far as vividness and intensity 

 go, it makes little difference to him whether his eyes are open or 

 shut what he sees is about the same in either case. But more 

 commonly the idea must be much heightened before it reaches 

 sensational intensity. Another friend of mine by thinking in- 

 tently of a friend's appearance can see that friend slowly taking 

 shape, at first as a shadowy outline, then gaining in clearness and 

 solidity until the shadowy outline has become the perfect form of a 

 real person. Now, if we regard the dimmest idea as zero and the 

 clear sensation as the maximum, we may say that any mental state 

 may conceivably run through all the intervening grades, and we 

 have reason to believe that every mental state tends to run through 

 some grades. This I would express by saying that every mental 

 state tends to develop within limits which we can not at present 

 assign. The first property of the mental state, then, is that of 

 development. It is of importance in explaining the phenomena 

 of dreams and hallucinations. 



The second group of properties which I shall mention depend 

 upon the transmissibility of the physical impulse. I have already 

 shown in my first paper how mental elements become agglutinated 

 into systems in which any one tends to awaken the others. It is 

 also true of the relation of any one system to another ; they tend 



