OF THE UNDERSTANDING 363 



The special organ in question, to which I have given the name of 

 hypocephalon, consists of two wrinkled pulpy hemispheres, investing 

 or covering that medullary region which I call more strictly the brain, 

 and which contains the nucleus or centre of communication of the 

 nervous system and gives rise to the nerves of the special senses ; the 

 cerebellum is a mere appendage of it. 



This region (the brain properly so-called, including the cerebellum) 

 and the hypocephalon are quite distinct from each other, especially as 

 regards their functions, although they are commonly confused together 

 under the general name of brain or encephalon. Now it is in the func- 

 tions of the hypocephalon alone that I shall seek the physical causes of 

 the various intellectual faculties, because this organ is the only one 

 that has the power of giving rise to them. 



Though not easily recognised, there is a real differentiation in the 

 parts of this organ. This differentiation and the varied movements 

 of the contained subtle fluid are the only origin of the different 

 intellectual acts which I have named. This is the general idea, which 

 I propose briefly to develop. 



At the outset, in order to introduce some order into our discussions 

 we must posit or recall the two following principles which are at the 

 base of all legitimate hypotheses on this subject. 



First principle : All intellectual acts whatever originate from ideas, 

 acquired either at the time or previously, for these acts may always 

 be reduced to ideas, or relations between ideas, or operations on 

 ideas. 



Second principle : Every idea of any kind originates either directly 

 or indirectly from a sensation. 



Of these two principles, the first is fuUy confirmed by an investiga- 

 tion as to what the various acts of the imderstanding really consist 

 of ; in all such acts, ideas are invariably the subject or material of the 

 operations carried out. 



The second of these principles had been recognised by the ancients, 

 and is perfectly expressed in that axiom, which Locke has so success- 

 fully sustained, viz. : That there is nothing in the understanding which 

 was not 'previously in sensation. 



Hence it follows that every idea must in the last analysis be resolved 

 into an image perceived, and that since whatever is in our understand- 

 ing came there vid sensation, aU that issues from it and can find no 

 perceptible object to fasten upon is absolutely chimerical. This is the 

 obvious conclusion drawn by M. Naigeon from Aristotle's axiom. 



The axiom however is not yet universally admitted, for many people 

 hold on account of certain facts whose causes they do not perceive, 

 that there really are innate ideas. They persuade themselves that they 



