This paper examines how the questions raised by Rene Descartes in his "Meditations" of 1641 revolutionised the manner in which people considered various ideas, especially concerning God, the idea of the individual self and its existence, and the existence of material things.
From the Paper:
"The existence of matter is a rather perplexing subject to which there are a number of different beliefs and arguments. Descartes, who first breached this topic believed that he had lots of ideas in his head and they were not all created by himself, his sensations were not all his. Descartes believed that they came from God and that God would not deceive him and so therefore matter must exist. This was Descartes proof, and since in his previous meditation where he proves the existence of God, his argument does stand up."