Locke states his belief that everything we know to be true we have learned through experience by making a positive case for the opposite view, which is that no knowledge and indeed no principle of knowledge is innate, or not subject to the influence of experience. What is innate, for Locke, is what is imprinted on the mind, but he insists (Essay 68) that if it were imprinted on the mind the mind would be conscious of it. But the evidence of human development is that the inexperienced mind profoundly does not perceive, hence does not know, whatever imprint may be on it: "To say a notion is imprinted on the mind, and yet at the same time to say that the mind is ignorant of it and never yet took notice of it, is to make this impression nothing" (68-9).
Now of course the human mind eventually comes to have perception and knowledge of a notion. But the fact that human reason arrives at self-consciousness or "come[s] to the use of reason" (69) does not prove the innate quality of one, some, or all notions. Rather, it proves the opposite, according to Locke. This is because the acquisition and refinement of reason come about only by way of the extension of reason in the world, i.e., by way of pragmatic projection and tests of reason in the form of response to unfolding experience. Reason may discover truth, but the very process of discovery demonstrates that they are not innate. To suggest that discovery demonstrates that reason is discovering what it was hitherto ignorant of in its own mind is "in effect to say, that men know and know them [truths] not at the same time" (70). This is declared to be utterly impossible. Indeed, coming to the use of reason and discovering reason are nothing else than formulations of the project of learning through experience.
Leibniz's claim that some known things cannot be learned through experience is based on the view that all knowledge and perception lie implicit in the mind, or more exactly rational...