NOTES ON BOOLE'S LAWS OF THOUGHT*. 



IT appears to be assumed in Chapter m. Section 8, that in 

 deriving one conception from another the mind always moves, 

 so to speak, along the line of predicamentation, always passes 

 from the genus to the species. No doubt everything stands in 

 relation to something else, as the species to its genus, and con- 

 sequently the symbolical language proposed is in extent per- 

 fectly general, that is, it may be applied to all the objects in the 

 universe. But I venture to doubt whether it can express ex- 

 plicitly all the relations between ideas which really exist, all the 

 threads of connexion which lead the mind from one to the other. 

 It seems to me that the mind passes from idea to idea in accord- 

 ance with various principles of suggestion, and that in corre- 

 spondence with the different classes of such principles of sug- 

 gestion we ought to recognize different branches of the general 

 theory of inference. This leads me to a further doubt whether 

 logic and the science of quantity can in any way be put in 

 antithesis to one another. From the notion of an apple we may 

 proceed to that of two apples, and so on in a process of aggre- 

 gation, which is the foundation of the science of discrete quantity. 

 Or again, from the notion of an apple we may proceed to that 

 of a red apple, and this movement of the mind in lined predica- 

 mentali is the foundation of ordinary logic. But it is plain, 

 d, priori, that there are other principles of suggestion besides 

 these two, and the following considerations lead me to think 

 that there are other exercises of the reasoning faculty than those 

 included in the two sciences here referred to. 



In the first place, certain inferences not included in the ordi- 

 nary processes of conversion and syllogism were recognized as 

 exceptional cases by the old logicians. Leibnitz has mentioned 

 some with the remark that they do not depend on the dictum 



* Now first published. 



