DOCTBINE Or SENSITIVE PERCEPTION. 293 



proper theme, it is sufficient to observe that the philosopher whose 

 views we are expounding, assumes it as an axiom, that there can be 

 no sensation and of course no perception, except on condition of 

 plurality — plurality in this besides other respects, that the organic 

 affections apprehended in sensation be out of, or locally external to, 

 one another. 



"We are now in a position to understand the manner in which 

 scepticism regarding an external world is dealt with by Sir 

 William Hamilton. 



Strange as it may appear to " the vulgar," (we employ Dr. Eeid's 

 familiar expression in no disrespectful sense), that any person out of 

 a lunatic asylum should call in question the reality of external 

 objects, and hesitate to allow the existence of the friend whom he 

 beholds, of the food which he tastes, or of the wall against which he 

 knocks his head, Sir William Hamilton maintains, that on any 

 other doctrine than one of immediate perception, such scepticism 

 not only is natural, but becomes a logical necessity. It is a first 

 principle in philosophy that nothing should be believed, except it be 

 known, either immediately in consciousness, or mediately by in- 

 ference from data which consciousness affords. The Cartesian spirit, 

 which doubts whatever is not established — which relentlessly bars 

 out of the mind the most universally received maxims, so long as 

 they seek admittance in the guise of dogmas — whose stern decision 

 regarding every propositon affirming what is not either immediately 

 or mediately known, is, let it be rejected : this is the true philosophic 

 temper, not at all deserving the censure that has so often been 

 ridiculously passed upon it, but on the contrary worthy of the highest 

 commendation. Let, then, a student endowed with this disposition, 

 address himself to the subject of sensitive perception, starting with 

 the idealistic view, that we possess an immediate knowledge only of 

 what is in our minds. How shall he proceed ? Suppose that, sail- 

 ing down the St. Lawrence, he is admiring the strange and beauteous 

 spectacle of the Thousand Isles. The only thing of which he is 

 presumed to be immediately cognizant is a mental affection, a peculiar 

 sensation connected (the vulgar think) with the presence of certain 

 islands. But does the vulgar opinion — he, as a philosopher, is 

 necessitated to ask himself — rest upon a solid foundation ? Are 

 there really any islands in the case ? How does he know that ? 

 Should it be suggested that the sensations excited in him must have 

 a cause, the question will still occur, must the cause be an external 

 one ? Must it be material ? May not his sensations arise from his 

 own mental energy, unconsciously exerted ? May those subjective 



