As John Locke studied humans in his work “An Essay Concerning Human Understanding” he continually referenced Descartes for ideas as he asked this fundamental question: “When we are concerned with something about which we have no certain knowledge, what rules or standards should guide how confident we allow ourselves to be that our opinions are right?” A simpler way of putting it is how do humans know ideas, and what are the different types of ideas. An idea to Locke “can simply mean some sort of brute experience.” He shows that there are “No innate principles in the mind.”. Thus, he concludes that “our ideas are all experiential in nature.” An experience can either be a sensation or a reflection: “consider whether there are any innate ideas in the mind before any are brought in by the impression from sensation or reflection.” Therefore, an idea was an experience in which the human mind apprehended something.