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co-existence with it of that intellectual activity of which 

 it is the outward expression. 



But language reacts upon the mind of him who uses 

 it. Besides being an interpreter of thought, it exercises 

 a powerful influence on the process of thinking, (i) It 

 helps us to analyse new complex impressions by the 

 distinctness and definiteness which it has given to our 

 conceptions of previous impressions. (2) By memory 

 or writing it enables us to preserve the results of 

 mental activity for future service. (3) It greatly aids 

 mental processes by substituting a short word for a very 

 complex idea accompanied by a variety of mental 

 images. Signs, when their meaning is definitely 

 established, can be used as counters, and we can 

 temporarily neglect what they signify while we are 

 working with them till we come to a final result, as in 

 the case of arithmetical and algebraic signs, as we 

 saw in the second chapter.* (4) Finally language 

 serves, as every one knows, as a means of communica- 

 tion, and so has become an enormous factor in mental 

 development, since, as we have seen, the mental 

 development of each man depends directly on his 

 intellectual environment which appears absolutely 

 indispensable to it, although neglected children and 

 deaf mutes are saidf to be able to form a sort of 

 language for themselves. 



Just as all races of men are men, and exhibit no great 

 or essential structural or functional differences, so they 

 all possess the power of speech, although that power is 

 expressed in many different languages, each of which has 

 its own method of expression. In Latin one word, amavi, 



* See ante, pp. 12 and 23. 



t See " Origin of Human Reason," p. 232. 



