228 THE POPULAR SCIENCE MONTHLY. 



grade, we obtain, as it were, an. inclined plane of human intelligence, 

 which indicates the probable order in which the human faculties have 

 appeared during the history of their development ; and, on examining 

 this inclined plane of human intelligence, we find that it runs sugges- 

 tively parallel with the inclined plane of animal intelligence, as we 

 descend from the higher to the lower forms of psychical life. 



I have only time to treat of one other branch of my subject. Be- 

 lieving, as I have said, that language, or the logic of signs, plays so 

 essential a part in developing the higher intellectual life of man, it 

 occurred to me that a valuable test of the truth of this view was to be 

 found in the mental condition of uneducated deaf-mutes. It often hap- 

 pens that deaf and dumb children of poor parents are so far neglected 

 that they are never taught finger-language, or any other system of 

 signs, whereby to converse with their fellow-creatures. The conse- 

 quence, of course, is that these unfortunate children grow up in a state 

 of intellectual isolation, which is almost as complete as that of any of 

 the lower animals. Now, when such a child grows up and falls into the 

 hands of some competent teacher, it may, of course, be educated, and 

 is then in a position to record its experiences when in its state of intel- 

 lectual isolation. I have, therefore, obtained all the evidence I can as 

 to the mental condition of such persons, and I find that their testimony 

 is perfectly uniform. In the absence of language, the mind is able to 

 think in the logic of feelings, but can never rise to any ideas of higher 

 abstraction than those which the logic of feelings supplies. The un- 

 educated deaf-mutes have the same notions of right and wrong, cause 

 and eflFect, and so on, as we have already seen that animals and idiots 

 possess. They always think in the most concrete forms, as shown by 

 their telling us when educated that so long as they were uneducated 

 they always thought in pictures. Moreover, that they cannot attain to 

 ideas of even the lowest degree of abstraction, is shown by the fact that 

 in no one instance have I been able to find evidence of a deaf-mute 

 who, prior to education, had evolved for himself any form of supernat- 

 uralism. And this, I think, is remarkable, not only because we might 

 fairly suppose that some rude form of fetichism, or ghost-worship, 

 would not be too abstract a system for the unaided mind of a civilized 

 man to elaborate, but also because the mind in this case is not wholly 

 unaided.' On the contrary, the friends of the deaf-mute usually do 

 their utmost to communicate to his mind some idea of whatever form of 

 religion they may happen to possess. Yet it is uniformly found that, 

 in the absence of language, no idea of this kind can be communicated. 



^ Were it not for certain criticisms which have appeared on my lecture as originally 

 delivered, I should have thought it unnecessary to point out that an uneducated deaf- 

 mute inherits the cerebral structure of a man. The fact, therefore, of his having human 

 feelings and expressions of face, as well as the capacity for education, is no proof that 

 language is not necessary for the formation of abstract ideas, unless it could h^ proved 

 that the human brain might have been what it is, even if the human race had never 

 evolved any system of language. 



