The most direct and in a sense the most important problem that our conscious knowledge of nature should enable us to solve is the anticipation of future events, so that we may arrange our present affairs in accordance with such anticipation. 1 As a basis for the solution of this problem we always make use of our knowledge of events that have already occurred, obtained by chance observation or by prearranged experiment. In thus endeavoring to draw inferences about the future from the past, we always adopt the following process. We form for ourselves mental pictures or symbols of external objects 2 ; and the form that we give them is such that the necessary consequents in thought of our pictures are always the pictures of the necessary 324consequents in nature of the objects pictured. 3 In order that this requirement may be satisfied, there must be a certain conformity between nature and our thought. Experience teaches us that this requirement can be satisfied, and hence that such a conformity does in fact exist. When on the basis of our accumulated previous experiences we have once succeeded in constructing pictures with the desired properties, we can quickly derive by means of them, as by means of models, 4 the consequents which in the external world occur only after a comparatively long time, or as the result of our own intervention. We are thus able to be in advance of the facts, and to decide as to present affairs in accordance with the insight so obtained. The pictures of which we here speak are our models of things; these models are in conformity with the things themselves in one important respect, namely, in satisfying the above-mentioned requirement. For our purpose it is not necessary that they should be in conformity with the things in any other respect whatsoever. As a matter of fact, we do not know, nor have we any means of knowing, whether our models of things are in conformity with the things themselves in any other than this one fundamental respect.