In meditation three Descartes attempts to prove the existence of God. Descartes is not quick to make a decision on the existence of God because of human error that arises within our judgement. Descartes then slowly dissects the whole situation. Descartes realizes that his ideas may come from different entities, "But among these ideas, some appear to me to be innate, some adventitious, and others to be formed by myself." (Descartes 116) He then sees that an idea of God cannot come from nothing, which leads me to Descartes causal principal, "And from this it follows, not only that something cannot proceed from nothing, but likewise that what is more perfect-that is to say, which has more reality within itself-cannot proceed from the less perfect." (Descartes 118) There must be a creator and therefore an infinite perfect being and therefore a God. Also God cannot be a deceiver because if God were a deceiver this would be an imperfection and this is not in Gods nature. And finally Descartes attempts to prove the existence of material substances in meditation six. Descartes starts out by telling us that in all probability there is a body and material things but that he is not certain. Material substances exist because, "God is no deceiver, it is very manifest that He does not communicate to me these ideas immediately and by Himself, nor yet by the intervention of some creature in which their reality is not formally, but only eminently, contained." (Descartes 131) Corporeal things exist because God has given us no reason to doubt him and therefor our perceptions of these things must come from the things themselves.
George Berkeley has very similar beliefs to that of Descartes but has different reasons for believing them. Berkeley has a very idealist view of things; he believes that there are no material things and that there are only minds that exist. Berkeley says that there is no possible way to prove the existence of corporeal things.