Let us next consider how this question stands as to the conceptions he entertains respecting the minds of other men. That which gives him the sensation of colour, is not any thing coloured out of himself; and that which gives him the sensation of length, breadth and thickness, is not any thing long, broad and thick in a manner corresponding with the impression he receives. There is nothing in the nature of a parallel, a type and its archetype, between that which is without him and that which is within, the impresser and the impression. This is the point supposed to be established by Locke and Newton, and by those who have followed the reasonings of these philosophers into their remotest consequences. But the case is far otherwise in the impressions we receive respecting the minds of other men. In colour it has been proved by these authors that there is no express correspondence and analogy between the cause of the sensation and the sensation. They are not part and counterpart. But in mind there is a precise resemblance and analogy between the conceptions we are led to entertain respecting other men, and what we know of ourselves. I and my associate, or fellow-man, are like two instruments of music constructed upon the same model. We have each of us, so to speak, the three great divisions of sound, base, tenor and treble. We have each the same number of keys, capable of being struck, consecutively or with alternations, at the will of the master. We can utter the same sound or series of sounds, or sounds of a different character, but which respond to each other. My neighbour therefore being of the same nature as myself, what passes within me may be regarded as amounting to a commanding evidence that he is a real being, having a proper and independent existence. There is further something still more impressive and irresistible in the notices I receive respecting the minds of other men. The sceptics whose reasonings I am here taking into consideration, admit, each man for himself, the reality of his own existence. There is such a thing therefore as human nature; for he is a specimen of it. Now the idea of human nature, or of man, is a very complex thing. He is in the first place the subject of sensible impressions, however these impressions are communicated to him. He has the faculties of thinking and feeling. He is subject to the law of the association of ideas, or, in other words, any one idea existing in his mind has a tendency to call up the ideas of other things which have been connected with it in his first experience. He has, be it delusive or otherwise, the sense of liberty of action. But we will go still further into detail as to the nature of man.