Mental Processes in Man. 305 



bygone influences of the environment shadows or after- 

 images of previous modes of influence. Without this 

 process of registration and revival, stimuli could never 

 give rise to sensations and perceptions such as we know 

 them. Without it experience would be impossible. 



We may say, then, that impressions (resulting from 

 stimuli) and their revival in memory are the bricks of the 

 house of knowledge ; and these' are built up through ex- 

 perience into what we call the world of things around 

 us. There may be and is a certain amount of mortar, 

 supplied by the builder, in addition to the elementary 

 bricks. But without the bricks no house of knowledge 

 could be built. Let us now examine the bricks and the 

 building. 



From what we have already learnt in the chapter on 

 " The Senses of Animals," it is clear that the impressions 

 and their revivals in memory have differences in quality. 

 Here, on the very threshold of the subject, we must pause. 

 They have differences of quality. But in consciousness 

 these differences must be distinguished. And this involves 

 their recognition and discrimination, presupposing, there- 

 fore, a corresponding faculty, however simple, on the part 

 of the recipient. Without cognition and recognition (twin 

 sisters, born in the same hour) we can never get beyond 

 mere impressions; which may, indeed, be differentiated 

 physically, as different stimuli due to diverse action of the 

 environment, but are psychically undifferentiated. This 

 recognition and discrimination is thus the primary activity 

 of the recipient mind. Here is already some of the mortar 

 supplied by the builder. Memory is absolutely essential to 

 the process. The sense-impression of external origin gives 

 rise to an impression of similarity or dissimilarity, which is 

 part of the internal reaction to the external stimulus. 

 Thus impressions are raised to the level of sensations. A 

 sensation is an impression that has been discriminated 

 from others, and recognized as being of such and such a 

 nature. The impressions of the sense-organs as we know 

 them are thus not mere impressions, but impressions 



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