CHAPTER II
THE POSSIBILITY OF ENLARGING OUR KNOWLEDGE OF MEMORY
Section 4. The Method of Natural Science
The method of obtaining exact measurements—i.e., numerically exact ones—of the inner structure of causal relations is, by virtue of its nature, of general validity. This method, indeed, has been so exclusively used and so fully worked out by the natural sciences that, as a rule, it is defined as something peculiar to them, as the method of natural science. To repeat, however, its logical nature makes it generally applicable to all spheres of existence and phenomena. Moreover, the possibility of defining accurately and exactly the actual behavior of any process whatever, and thereby of giving a reliable basis for the direct comprehension of its connections depends above all upon the possibility of applying this method.
We all know of what this method consists: an attempt is made to keep constant the mass of conditions which have proven themselves causally connected with a certain result; one of these conditions is isolated from the rest and varied in a way that can be numerically described; then the accompanying change on the side of the effect is ascertained by measurement or computation.
Two fundamental and insurmountable difficulties, seem, however, to oppose a transfer of this method to the investigation of the causal relations of mental events in general and of those of memory in particular. In the first place, how are we to keep even approximately constant the bewildering mass of causal conditions which, in so far as they are of mental nature, almost completely elude our control, and which, moreover, are subject to endless and incessant change? In the second place, by what possible means are we to measure numerically the mental processes which flit by so quickly and which on introspection are so
