Summary In asking where we get our idea of substances, Locke finds himself in one of the stickier sections of the Essay. He gives us the following picture of the origin of our ideas of substances: As we go through the world we carve up the dense sensory array into discrete objects, noticing which qualities regularly seem to cluster together.
Summary Having developed in Book I his argument concerning the nonexistence of innate ideas, Locke undertakes in Book II to describe in detail the process by means of which ideas come to be present in human minds. His fundamental thesis is that experience alone is adequate to account for all the ideas included in anyone's store of knowledge.
There are some passages in the Essay Concerning Human Understanding which indicate that Locke accepted this type of skepticism. He was always anxious to avoid the appearance of dogmatism, and this may have been one of the reasons why in some instances he was careful not to make any definite statement about the nature of the outside world.
But yet after all, I think I may, without injury to human perfection, be confident, that our knowledge would never reach to all we might desire to know concerning those ideas we have; nor be able to surmount all the difficulties, and resolve all the questions that might arise concerning any of them.