A Little History of Philosophy (Little Histories)

by Nigel Warburton

he convinced himself that the idea of God proves God's existence – God wouldn't be perfect unless he was good and existed, just as a triangle wouldn't be a triangle without interior angles adding up to 180 degrees. Another of his arguments, the Trademark Argument, suggested that we know God exists because he has left an idea implanted in our minds – we wouldn't have an idea of God if God didn't exist. Once he was certain that God existed, the constructive phase of Descartes' thought became much easier. A good God wouldn't deceive humanity about the most basic matters. So, Descartes concluded, the world must be more or less as we experience it. When we have clear and distinct perceptions these are reliable. His conclusion: the world exists, and is more or less as it appears, even though we sometimes make mistakes about what we perceive. Some philosophers, however, believe this was wishful thinking, and that his evil demon might just as easily have deceived him about God's existence as about the thought that 2 + 3 = 5. Without the certainty of a good God's existence, Descartes would not have been able to move beyond his knowledge that he was a thinking thing. Descartes believed that he had shown a way out of complete scepticism; but his critics are still sceptical about this.