Nawd asked:

Descartes, drawing on the success of the Copernican system, believes that many of his former beliefs must be false. How worried should we be about the fact that the world is not exactly as it seems?

Answer by Helier Robinson

Philosophy begins with the discovery that the world is not exactly as it seems. This is not a worry (unless you are deeply committed to your common sense beliefs) but it must be a concern, philosophically. One of the things about beliefs is that each one carries a piggy-back belief, a belief that the first belief is true. Everyone might say that ‘Other people have false beliefs but I do not, because all my beliefs are true: I would not believe them if they were false’. But if, rationally, you try to get away from this naive egocentricity, how do you decide which of your beliefs are false? The answer seems to be that you need to study both science and philosophy; you need both because scientists tend to be philosophically naive and philosophers, these days, tend to be scientifically naive (particularly with regard to the mathematical sciences). That’s quite a lot of study. Good luck!