68o POPULAR SCIENCE MONTHLY. 



truism in the public mind that a mere specialist grows more nar- 

 row every day of his life, and there seems to be plenty of evidence 

 in one's environment to give rise to such speculation. The argu- 

 ment in favor of liberal culture before a man takes up his spe- 

 cialty is based upon a recognition of the fact that knowledge of 

 one kind only predetermines a man to be able to appreciate and 

 interpret things of a similar nature, and these merely. There are 

 two reasons for this, as one can readily see from a little study of 

 humanity around him. In the first place, what a man knows 

 determines what he is interested in ; and common-sense philosophy 

 has often declared that people are essentially selfish, because they 

 are interested only in their own kinds of business, their own pur- 

 suits, their own specialties, and they lack that many-sided interest 

 which is necessary for any title to unselfishness. The lawyer feels 

 little interest in what the medical fraternity are doing, and per- 

 haps will never be seen at a medical lecture ; the scholar, pure 

 and simple, troubles himself little about questions of government, 

 and is a very insignificant warrior indeed in the political camp. 

 The mechanic reads theology or listens to a theological sermon 

 with the greatest difficulty. But each of these types has the deep- 

 est interest for readings, lectures, and everything else that relate 

 to his own specialty, or to the thing he is most familiar with. It 

 sometimes happens, it is true, that a poet may be interested in 

 psychology or theology, but this is the case only when he is 

 already well versed upon these subjects ; and other apparent 

 exceptions to the general rule may probably be explained in the 

 same way. 



The second point in proof of this law, that what one knows 

 determines what he can get to know, is that, psychologically 

 speaking, ideas create the ability to appreciate and interpret other 

 ideas of a similar nature. This also may be abundantly illus- 

 trated by the circumstances of daily life. A man very widely 

 read in history may be unable to understand a lecture upon 

 biology, mechanics, or any subject unrelated to history. The 

 general power which he has accumulated in his historical re- 

 searches can not be applied to the ready and easy mastery of all 

 sorts of things, as the old psychology stoutly maintained. Again, 

 one who has pursued mathematical studies to great length is 

 not thereby qualified to become a statesman ; the power which 

 may be generated by the study of mathematics is not transferable 

 immediately to the solution of social problems. Educational 

 psychology, then, may be said to declare in a very broad way 

 that ideas create capacity for the reception of ideas of similar 

 kind, but that there is practically no such thing as the acquisition 

 of general power by the mastery of special subject-matter. In 

 explanation of this practically, it should be said that any kind of 



