But leaving the question of _what may or may not be_, for that other _what actually is_, I desire those philosophers, who pretend that we have an idea of the substance of our minds, to point out the impression that produces it, and tell distinctly after what manner that impression operates, and from what object it is derived. Is it an impression of sensation or reflection? Is it pleasant, or painful, or indifferent? Does it attend us at all times, or does it only return at intervals? If at intervals, at what times principally does it return, and by what causes is it produced? If, instead of answering these questions, any one should evade the difficulty, by saying, that the definition of a substance is _something which may exist by itself_, and that this definition ought to satisfy us: should this be said, I should observe, that this definition agrees to every thing that can possibly be conceived; and never will serve to distinguish substance from accident, or the soul from its perceptions. For thus I reason. Whatever is clearly conceived, may exist; and whatever is clearly conceived, after any manner, may exist after the same manner. This is one principle which has been already acknowledged. Again, every thing which is different is distinguishable, and every thing which is distinguishable is separable by the imagination. This is another principle. My conclusion from both is, that since all our perceptions are different from each other, and from every thing else in the universe, they are also distinct and separable, and may be considered as separately existent, and may exist separately, and have no need of any thing else to support their existence. They are therefore substances, as far as this definition explains a substance. Thus, neither by considering the first origin of ideas, nor by means of a definition, are we able to arrive at any satisfactory notion of substance, which seems to me a sufficient reason for abandoning utterly that dispute concerning the materiality and immateriality of the soul, and makes me absolutely condemn even the question itself. We have no perfect idea of any thing but of a perception. A substance is entirely different from a perception. We have therefore no idea of a substance. Inhesion in something is supposed to be requisite to support the existence of our perceptions. Nothing appears requisite to support the existence of a perception. We have therefore no idea of inhesion. What possibility then of answering that question, _Whether perceptions inhere in a material or immaterial substance_, when we do not so much as understand the meaning of the question?