Locke distinguished in the Essay on Human Understanding two kinds of ideas: ideas simple and complex ideas.
Simple ideas are mixed in the sensible object perceived. He understands that the white and cold snow are distinct qualities simple: “nothing is more obvious to a man that clear and distinct perception he has of those simple ideas.” These are “all the materials of our knowledge.” The mind can combine these simple ideas, and make complex ideas “when the mind has once received these simple ideas, it has the power to repeat, compare, to unite them together with an almost infinite variety , and thereby to form new complex ideas.
In both cases, the idea is a perception, or of sensible bodies, or operations of the mind.
This is why “having ideas, and perceptions have, one and the same thing.” We see once again affirmed the empiricism of Locke, which supports this view of the mind as a tabula rasa.
Locke shows that man can discover all the ideas by the mere use of his natural faculties.
Thus, man is not born with the idea of red, but he acquires it through the view.
If the primary qualities are in bodies, and thus are similar to the ideas we have, secondary qualities are not really in things, and ideas that we do not correspond to reality.
To better understand this idea, Locke is an example: “This is sweet, blue or hot in the idea is nothing in the body which we give these names a certain size, shape and particle motion insensitive which they are composed.
In fact, we take innate practical principles because we have not seen or that has forgotten its origin.
Looking good, “the doctrines that have no better sources than the superstition of a nurse or the authority of an old woman, become over time and by the consent of neighbors, many principles of religion and morality.