METHODS OF PHYSIOLOGICAL RESEARCH 35 



its widest and most general sense. One indispensable condition 

 of the conception is the assumption that something exists. If we 

 make this assumption, if we have something real or actual, 

 a fixed point, then knowledge is simply the causal reduction of 

 all phenomena to this reality. We have a measure for knowledge 

 in the satisfying of our craving for causality ; and the latter will 

 necessarily be satisfied, when once we have placed all phenomena 

 in causal relation to the one reality. 



Nevertheless, an objection may here be raised. Let us suppose 

 that we have succeeded in reducing all phenomena to the one 

 reality. (This reality appears in the different philosophical 

 systems under very different names, such as God, thing-in-itself, 

 the unknown, etc. the terms are equivalent and without material 

 significance.) The question would then arise, whether our 

 craving for causality would be satisfied, or whether it would not 

 force us still farther to ask, What is this thing which exists, this 

 reality, the unknown, the thing-in-itself, God, or whatever it is 

 termed ? In the latter case, here, again, would be a limit to our 

 knowledge. If we understand it rightly, however, this limit would 

 be a logical error, a false conclusion. Our craving for causality 

 arose and became established in the course of evolution by the 

 continual reduction of effects to causes, and it is easily possible 

 that in the present case it would continue for awhile from inertia 

 to hold before us the question, why ? But it is evident that we 

 would thus be guilty of an error of reasoning ; for, if all phenomena 

 were reduced to the one reality, it would be a complete contra- 

 diction to wish to know that reality in terms of non-reality. The 

 demand that, after complete knowledge of the world, we must 

 know the world still more involves an evident absurdity. Hence, 

 the above objection is only an apparent one. 



We assume, therefore, the desire to reduce all phenomena to 

 that which is real. Then the question arises, What is real ? 



Here we come in contact with a mistaken view which is espe- 

 cially wide-spread in science and has been faithfully handed 

 down from primitive time as an heirloom from the childhood 

 of the human mind. This is the view that the physical 

 world existing outside of us and independent of our own mind is 

 real, and that, accordingly, we must reduce all phenomena to its 

 laws. The impossibility of such an undertaking is plainly shown 

 in the above argument of du Bois-Reymond. Yet a great many 

 men of science among those who, like du Bois-Reymond, have 

 reflected upon the limitations of human knowledge, we need 

 mention only the gifted botanist Nageli ('77) have held it to be 

 possible that even psychical phenomena may be resolved into the 

 processes of matter. Hence it is useful to clarify our ideas as to 

 what matter really is. 



At first sight bodies appear to us as actual objects outside of 



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