HOFFDING'S OUTLINES OF PSYCHOLOGY. 3 8 7 



ideas, there still remains a distinction between ideas of material movement and 

 ideas of phenomena of consciousness ; and thus again arises the problem how 

 these different sets of ideas, which have arisen in accordance with experience, 

 are to be combined. The problem for psychology is empirical, and is independent 

 of the metaphysical. We do not ask whether mind or matter is most funda- 

 mental ; we inquire in what way menta 1 and material phenomena are connected 

 in that experience which every system of metaphysics consciously or unconsciously 

 presupposes. 



The fourth possibility, the identity hypothesis, regards the 

 mental and the material worlds as two manifestations of one and 

 the same being, both given in experience. 



If it is contrary to the doctrine of persistence of force to suppose a transition 

 from the one province to the other, and if nevertheless the two provinces exist 

 in our experience as distinct, then the two sets of phenomena must be unfolded 

 simultaneously, each according to its own laws; so that for every phenomenon 

 in the world of consciousness there is a corresponding phenomenon in the world 

 of matter, and conversely. The parallels already drawn point directly to such a 

 relation ; and it would be an amazing accident if, while the characteristic marks 

 repeated themselves in this way, there were not at the foundation an inner con- 

 nection. Both the parallelism and proportionality between the activity of con- 

 sciousness and cerebral activity point to an identity at bottom. The difference 

 which remains in spite of the points of agreement compels us to suppose that one 

 and the same principle has found its expression in a double form. We have no 

 right to take mind and body for two beings in reciprocal interaction. We are, 

 on the contrary, impelled to conceive the material interaction between the ele- 

 ments composing the brain and nervous system as an outer form of the inner 

 ideal unity of consciousness. What we in our inner experience become conscious 

 of as thought, feeling, and resolution, is thus represented in the material world 

 by certain material processes of the brain, which as such are subject to the law 

 of the persistence of energy, although this law can not be applied to the relation 

 between cerebral and conscious processes. It is as though the same thing were 

 said in two languages. . . . 



In the mental as in the material world we hold fast the law of continuity. 

 The identity hypothesis regards both these worlds as two manifestations of one 

 and the same being, both given in experience. 



The two languages in which the same thought is here expressed, we are not 

 able to trace back to a common original language. So long as we keep strictly to 

 experience, one province is presented as a fragment while the other extends to 

 infinity. The doctrine of the persistence of energy makes the material world into 

 a totality which we can never measure, but in which the fate of the individual 

 forms and elements can be traced. The mental world has no corresponding law 

 to exhibit. Mental element^ come and go in experience without our being able 

 to point to an equivalent. The fact that mental states can not be measured like 

 physical energies and chemical substances is, in itself, sufficient to frustrate the 

 hope of our finding a mental parallel to the doctrine of the persistence of force. 

 But, in addition to this, even the fundamental conception of a mental existence 

 puts difficulties in the way. Material existences can pass one into another, so 

 that the energy lost in one is preserved in the other. The doctrine of the persist- 

 ence of energy shows us the unity and eternity of Nature during the coming and 

 going of all material beings ; but mental existence, as has been seen, has for its 



