His Essay Concerning Human Understanding
He had the idea that all humans were born with a blank mind
"Let us suppose the mind to be, as we say white paper, void of all characters, without any ideas. How comes it to be furnished? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from experience... Our observation, employed either about external sensible objects or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understanding with all the materials of thinking."