⇒ Descartes believed that he could prove his experience using logical reasoning alone
⇒ Essentially his idea was that if you can follow his method of systematic doubt - which involves doubting everything you learn from experience or your senses - then you must exist. Because you can't doubt or question your own existence unless something exists to do the doubting or questioning.
⇒ Not only did Descartes claim he could prove your own existence, but he also claimed he could prove the existence of God using logic/reasoning
⇒ His ontological argument for the existence of God, for example, went like this: