86 HABIT AND INTELLIGENCE. [chap. 



Waste is a is a necessary condition of organic life and growth. The 

 of otSc organism is not like a crystal, which simply acquires sub- 

 life : stance, and, when it has done growing, remains in a state 

 of molecular immobility. Both during growth and after 

 growth has ceased, the organism is constantly losing sub- 

 stance and replacing it with new substance. Every one is 

 aware that this is true of the organism. Every one knows 

 that waste is not an imperfection of the organism, as 

 wearing-out is of machinery, but a necessary condition 

 of life. But it appears to be the general belief, that the 

 corresponding fact in mental life — the liability to lose 

 impressions by forgetting them — is an imperfection and a 

 weakness of mind, as liability to wear and tear is of 

 machinery. I am convinced that this is an error ; I am 

 so is for- convinced that as waste, no less than nutrition, is necessary 

 g'^^^Y^^ °*^ *o *^^^ l^f^ ^^^ growth of the organism, so forgetting, no 

 life. less than remembering, is necessary to the life and growth 

 of the mind. This may appear a strange paradox, but I 

 think that on consideration it will become evident. 

 If we If we remembered all the mental impressions we had 

 bered" ^'^'^^ received since the beginning of our mental life, we 

 every- should be distracted by their multitude, we should be 

 could not overwhelmed by their weight. If the sound of every 

 think. word of our own language, or of any other language with 

 which we have become familiar, were to recall to memory 

 every time we had ever heard it pronounced; or if the 

 sight of every familiar face were to recall every time we 

 had ever seen it ; if all details, the most insignificant as 

 well as the most important, the least interesting as well as 

 the most interesting, were to come crowding unbidden into 

 memory whenever we desired to think of any object or of 

 any event, — the mind would, as it were, have no room to 

 move, and thought would be impossible. But such a result 

 is prevented by that constitution of the memory in virtue 

 of which we retain, generally and on the average, the im- 

 portant and interesting particulars of any object or of any 

 event, and forget the rest ; so that, on the whole, we retain 

 what we need to retain, and forget what we do best to 

 forget. 



