DOCTRINE OP SENSITIVE PERCEPTION. 297 



of necessity, and the reference which writers like Brown make to the 

 irresistible belief that all men have of an external world. What Brown 

 speaks of is a persuasion of the existence of an object which is not 

 known, and possibly may be non-existent. On the other hand, the 

 necessity which those who hold the non-ego to be revealed in con- 

 sciousness, allege in support of their views, is just consciousness 

 irresistibly asserting itself. Should it be said that, on this view, the 

 application of the criterion of necessity to settle the question in 

 dispute, involves a petiiio principii — inasmuch as the conclusion 

 sought to be established is proved by an appeal to a test, the affirma- 

 tion of which is not substantially different from the affirmation of 

 the conclusion ; we answer that this objection would undoubtedly be 

 valid, were the immediacy of our apprehension of an external world 

 supposed to be proved (in the proper sense of the term) by the 

 criterion mentioned. But this is not meant. All that is meant is, 

 that the consciousness of an external world irresistibly asserts itself. 

 A datum of consciousness cannot (strictly speaking) be proved by 

 argument to be so ; it must be immediately known as such; and if 

 any one deny that a truth, which really forms one of the data of con- 

 sciousness, is entitled to be regarded in that light, we must content 

 ourselves with requesting him to purge his reflective eye with 

 " euphrasy and rue," and to think again. Tf he do so, well. He 

 will then recognise, without argument, what even now amidst his 

 hallucination, he is knowing, and irresistibly feeling that he knows. — 

 If not, his scepticism cannot be helped ; reasoning will never drive 

 it out of him ; he must be permitted to enjoy it. 



Neither Cosmothetic Idealists, nor those who, like Sir W. Hamil- 

 ton, plead for an immediate apprehension of the external world, 

 suppose that we know matter as absolutely existing ; both parties 

 agree that only its properties are known. From the earliest time, a 

 two-fold distinction among the properties of matter had been recog- 

 nized, corresponding more or less nearly (as stated by different 

 writers) with Locke's distribution of the qualities of bodies into 

 primary and secondary. Sir W. Hamilton adopts a new division ; 

 making three distinct classes of qualities, the primary, the secondary, 

 and .the secundo-primary ; the last being so called, because they 

 possess a double phasis, partaking in one aspect of the nature of the 

 primaries, and in another of that of the secondaries. The grounds 

 on which Sir "William proceeds in this entirely original arrangement 

 may be in a measure anticipated from what has been said ; and a 

 brief notice of his classification, will virtually involve a summary 

 VOL. II. — tr 



