This substance must be either God or an external extended body. God is no deceiver. He created me and gave me a great inclination to believe that these ideas come from corporeal things. If they do not come from external objects, then God must be a deceiver. But this is an absurdity.
Material objects exist.
These objects, however, may not be as they seem to us through the senses. Having established the existence of external objects, Descartes goes on to consider whether our senses tell us the truth about them. The relation of Mind and Body. I am intimately joined with my body. Feelings of pain and pleasure are confused modes of perception arising out of my union with the body.