THE LOGICAL MACHINE. 127 



Disjunctive propositions are to be treated in an exactly 

 similar manner. Thus, to work the premises 



A = AB I AC 

 B t C = BD t CD, 

 it is only necessary to press in succession the keys 



A (subj.), copula, A (pred.), B, | A,C, full stop. 

 B (subj.), t C, copula, B (pred.), D, | , C, D, full stop. 

 The combinations then remaining will be as follows 

 ABCD aBCD 

 ABcD aBcD 

 A&CD a&CD 

 afoD 

 abed. 



On pressing the subject key A, all the possible com- 

 binations which do not contain A will disappear, and the 

 description of A may be gathered from what remains, 

 namely that it is always D. The full-stop key restores 

 all combinations consistent with the premises and any 

 other selection may be made, as say not-D, which will 

 be found to be always not- A, not-B, and not-C. 



At the end of every problem, when no further questions 

 need be addressed to the machine, it is desirable to press 

 the Finis key, which has the effect of bringing into view 

 the whole of the conceivable combinations of the abece- 

 darium. This key in fact obliterates the conditions im- 

 pressed upon the machine by moving back into their 

 ordinary places those combinations which had been re- 

 jected as inconsistent with the premises. Before begin- 

 ning any new problem it is requisite to observe that 

 the whole sixteen combinations are visible. After the 

 Finis key has been used the machine represents a mind 

 endowed with powers of thought, but wholly devoid 

 of knowledge. It would not in that condition give any 

 answer but such as would consist in the primary laws 

 of thought themselves. But when any proposition is 



