Descartes’s best work is “Meditations on First Philosophy” which is where most of his investigation on the questions of knowing takes place. In meditation I Descartes accepts that he has learned throughout his life with his senses
but with reasons of doubt. He believes that we should not trust our senses entirely for they can mislead us regarding things that are simply observable. Even dreams are linked to reality because one portrays the representation of the other to conform that what forms in one is the duplication of the other.
In Meditation II Descartes goes the direction in trying to focus on what he can tell is certain and true. The problem that he raises are the problem of the sources of knowledge. By convincing himself that all other things does not exist, he finally reflected that him who thinks exists. That proof cannot be used for someone else if you are declaring it. Descartes’ Cogito Argument pushed many philosophers towards the belief that they can only trust their own existence is true. He found the sources of knowledge not from his senses but reason.
Two schools of thoughts came about following Descartes’ footsteps but both use different source. The rationalist believed that knowledge claims derive from sense of reason while empiricist were the opposite and use their senses as source of knowledge. John Lock, an empiricist, had a new argument against rationalist that a birth we are all born in a blank slate. We are who we are because of what we see and go through in our lives. It is not reasoning that is the source of our knowledge. Locke answers his questions in “Essay Concerning the Human Understanding” by proving that it is experience that shapes a person to who they are.