Think of how people respond to different methods of teaching. The effective teaching methods clear up understanding of something already within your mind. Also think of the feeling you have when you understand a good lesson. You"re not suddenly learning everything at once but realizing you already had that knowledge within you. Descartes believes that: the most certain knowledge anyone can have is the knowledge of one"s own existence as a. Existence can"t be doubted because process of doubting presupposes being a self (this process is otherwise known as systematic doubt). In terms of language, the words i am, i exist are true whenever anyone says it. Impossibility of doubting things seem to be the case, but experiences are always present and immediately accessible to us. Main idea: something remains the same even through all of its transformations. Descartes believes that: senses give us a level of understanding and knowledge that animals have, but our mind is different: example.