Nor must we omit, on this occasion, our accustomed method of examining ideas by considering those impressions from which they are derived. The impressions which enter by the sight and hearing, the smell and taste, are affirmed by modern philosophy to be without any resembling objects; and consequently the idea of solidity, which is supposed to be real, can never be derived from any of these senses. There remains, therefore, the feeling as the only sense that can convey the impression which is original to the idea of solidity; and, indeed, we naturally imagine that we feel the solidity of bodies, and need but touch any object in order to perceive this quality. But this method of thinking is more popular than philosophical, as will appear from the following reflections. First, 'tis easy to observe, that though bodies are felt by means of their solidity, yet the feeling is a quite different thing from the solidity, and that they have not the least resemblance to each other. A man who has the palsy in one hand has as perfect an idea of impenetrability, when he observes that hand to be supported by the table, as when he feels the same table with the other hand. An object that presses upon any of our members meets with resistance; and that, resistance, by the motion it gives to the nerves and animal spirits, conveys a certain sensation to the mind; but it does not follow that the sensation, motion and resistance, are any ways resembling. Secondly, the impressions of touch are simple impressions, except when considered with regard to their extension; which makes nothing to the present purpose: and from this simplicity I infer, that they neither represent solidity, nor any real object. For let us put two cases, viz. that of a man who presses a stone or any solid body with his hand, and that of two stones which press each other; 'twill readily be allowed that these two cases are not in every respect alike, but that in the former there is conjoined with the solidity a feeling or sensation of which there is no appearance in the latter. In order, therefore, to make these two cases alike, 'tis necessary to remove some part of the impression which the man feels by his hand, or organ of sensation; and that being impossible in a simple impression, obliges us to remove the whole, and proves that this whole impression has no archetype or model in external objects; to which we may add, that solidity necessarily supposes two bodies, along with contiguity and impulse; which being a compound object, can never be represented by a simple impression. Not to mention, that, though solidity continues always invariably the same, the impressions of touch change every moment upon us, which is a clear proof that the latter are not representations of the former.