He as a thinking thing is a property that is known to him. His mind differs in property than his brain. Proves metaphysical dualism (mind is different than the body: more certain of what occurs in own mind than what occurs outside (mind over body). Knowledge of his mind and not the world around him. Descartes knows his mind is a thing a mental substance: mind can expose itself to itself creating ideas of all different kinds of things there are. Can"t think of redness without something being red) existed so it didn"t need to be brought up (i. e. god: rate of reality: (highest) infinite -> substances -> properties (lowest) How did he get these ideas: got in his mind by being caused by what the ideas resemble; accurate, defects in his sense organs, insanity, tricked, etc. pictures of the world around him.