128 THE PRINCIPLES OF SCIENCE. 



worked upon the keys, the machine analyses or digests 

 the meaning of it and becomes charged with the know- 

 ledge embodied in that proposition. Accordingly it is 

 able to return as an answer any description of a term 

 or class so far as furnished by that proposition in ac- 

 cordance with the Laws of Thought. The machine is 

 thus the embodiment of a true logical system. The com- 

 binations are classified, selected or rejected just as they 

 should be by a reasoning mind, so that at each step in 

 a problem, the abecedarium represents the proper con- 

 dition of a mind exempt from mistake. It cannot be 

 asserted indeed that the machine entirely supersedes the 

 agency of conscious thought ; mental labour is required 

 in interpreting the meaning of grammatical expressions 

 and in correctly impressing that meaning on the machine ; 

 it is further required in gathering the conclusion from 

 the remaining combinations. Nevertheless the true pro- 

 cess of logical inference is actually accomplished in a 

 purely mechanical manner. 



It is worthy of remark that the machine can detect 

 any self-contradiction existing between the premises pre- 

 sented to it, for it will then be found that one or more 

 of the terms disappear entirely from the abecedarium. 

 Thus if we worked the two propositions, A is B, and 

 A is not>B, and then inquired for a description of A, 

 the machine would refuse to give it by exhibiting no 

 combination at all containing A. This result is in agree- 

 ment with the law which I have explained that every 

 term must have its negative (p. 88). Accordingly when- 

 ever any one of the letters A, B, C, D, a, b, c, d wholly 

 disappears from the abecedarium, it may be safely inferred 

 that some self-contradiction has been committed in the 

 premises. 



It ought to be carefully observed that the logical 

 machine cannot receive a simple identity of the form 



