It is the principal doctrine of Locke that all ideas are derived from sensation and reflection. He acknowledges that "it is a received doctrine that men have native ideas and original characters stamped upon their minds in their very first being;" but he utterly rejects every such theory. It is his principal business to protest and argue against the existence of such "innate ideas." Virtue he believes to be generally approved because it is profitable, not on account of any natural leaning of the mind in its direction. Conscience "is nothing else but our own opinion or judgment of the moral rectitude or pravity of our own actions." Memory is the power in the mind to revive perceptions which it once had, with this additional perception annexed to them, that it has had them before. Wit lies in the assemblage of ideas, judgment in the careful discrimination among them. "Things are good or evil only in reference to pleasure or pain;" ... "our love and hatred of inanimate, insensible beings is commonly founded on that pleasure or pain which we receive from their use and application any way to our senses, though with their destruction; but hatred or love of beings incapable of happiness or misery is often the uneasiness or delight which we find in ourselves, arising from a consideration of their very being or happiness. Thus the being and welfare of a man's children or friends, producing constant delight in him, he is said constantly to love them. But it suffices to note that our ideas of love and hatred are but dispositions of the mind in respect of pleasure or pain in general, however caused in us." We have no clear idea of substance nor of spirit. Substance is that wherein we conceive qualities of matter to exist; spirit, that in which we conceive qualities of mind, as thinking, knowing, and doubting. The primary ideas of body are the cohesion of solid, and therefore separate parts, and a power of communicating motion by impulse. The ideas of spirit are thinking and will, or a power of putting body into motion by thought, and, which is consequent to it, liberty. The ideas of existence, mobility, and duration are common to both.