The persons then, who refine with Berkeley upon the system of things so far, as to deny that there is any such thing as matter in the sense in which it is understood by the writers on natural philosophy, proceed on the ground of affirming that we have no reason to believe that the causes of our sensations have an express resemblance to the sensations themselves(81). That which gives us a sensation of colour is not itself coloured: and the same may be affirmed of the sensations of hot and cold, of sweet and bitter, and of odours offensive or otherwise. The immaterialist proceeds to say, that what we call matter has been strewn to be so exceedingly porous, that, for any thing we know, all the solid particles in the universe might be contained in a nutshell, that there is no such thing in the external world as actual contact, and that no two particles of matter were ever so near to each other, but that they might be brought nearer, if a sufficient force could be applied for that purpose. From these premises it seems to follow with sufficient evidence, that the causes of our sensations, so far as the material universe is concerned, bear no express resemblance to the sensations themselves. (81) See above, Essay XXI. How then does the question stand with relation to mind? Are those persons who deny the existence of matter, reduced, if they would be consistent in their reasonings, to deny, each man for himself, that he has any proper evidence of the existence of other minds than his own? He denies, while he has the sensation of colour, that there exists colour out of himself, unless in thinking and percipient beings constituted in a manner similar to that in which he is constituted. And the same of the sensations of hot and cold, sweet and bitter, and odours offensive or otherwise. He affirms, while he has the sensation of length, breadth and thickness, that there is no continuous substance out of himself, possessing the attributes of length, breadth and thickness in any way similar to the sensation of which he is conscious. He professes therefore that he has no evidence, arising from his observation of what we call matter, of the actual existence of a material world. He looks into himself, and all he finds is sensation; but sensation cannot be a property of inert matter. There is therefore no assignable analogy between the causes of his sensations, whatever they may be, and the sensations themselves; and the material world, such as we apprehend it, is the mere creature of his own mind.