Now, returning to the idea of deception, it is a rather pernicious notion. Descartes wonders how God, an omnibenevolent being, could deceive him. It seems unlikely that s/he ever would. Moreover, if our senses are capable of being deceived then it must mean that we are imperfect. God’s design is supposed to be without fault and so it doesn’t entirely make sense for God to be the one doing the deceiving. Therefore, Descartes proposes the possibility that some all-powerful, malicious demon could be responsible for the deceit. This demon has the ability to make him doubt rationalist knowledge and he concludes now that even a priori knowledge can be doubted. Seen as Descartes has decided to be uncertain of everything, this demon idea is somewhat