It has already been pointed out, that Hume must have admitted, and in fact does admit, the possibility that the mind is a Leibnitzian monad, or a Fichtean world-generating Ego, the universe of things being merely the picture produced by the evolution of the phenomena of consciousness. For any demonstration that can be given to the contrary effect, the "collection of perceptions" which makes up our consciousness may be an orderly phantasmagoria generated by the Ego, unfolding its successive scenes on the background of the abyss of nothingness; as a firework, which is but cunningly arranged combustibles, grows from a spark into a coruscation, and from a coruscation into figures, and words, and cascades of devouring fire, and then vanishes into the darkness of the night.
On the other hand, it must no less readily be allowed that, for anything that can be proved to the contrary, there may be a real something which is the cause of all our impressions; that sensations, though not likenesses, are symbols of that something; and that the part of that something, which we call the nervous system, is an apparatus for supplying us with a sort of algebra of fact, based on those symbols. A brain may be the machinery by which the material universe becomes conscious of itself. But it is important to notice that, even if this conception of the universe and of the relation of consciousness to its other components should be true, we should, nevertheless, be still bound by the limits of thought, still unable to refute the arguments of pure idealism. The more completely the materialistic position is admitted, the easier is it to show that the idealistic position is unassailable, if the idealist confines himself within the limits of positive knowledge.
Hume deals with the questions whether all our ideas are derived from experience, or whether, on the contrary, more or fewer of them are innate, which so much exercised the mind of Locke, after a somewhat summary fashion, in a note to the second section of the _Inquiry_:--
"It is probable that no more was meant by those who denied innate ideas, than that all ideas were copies of our impressions; though it must be confessed that the terms which they employed were not chosen with such caution, nor so exactly defined, as to prevent all mistakes about their doctrine. For what is meant by _innate_? If innate be equivalent to natural, then all the perceptions and ideas of the mind must be allowed to be innate or natural, in whatever sense we take the latter word, whether in opposition to what is uncommon, artificial, or miraculous. If by innate be meant contemporary with our birth, the dispute seems to be frivolous; nor is it worth while to inquire at what time thinking begins, whether before, at, or after our birth. Again, the word _idea_ seems to be commonly taken in a very loose sense by Locke and others, as standing for any of our perceptions, our sensations and passions, as well as thoughts. Now in this sense I should desire to know what can be meant by asserting that self-love, or resentment of injuries, or the passion between the sexes is not innate?