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, I, 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 



