How do we know that anything really exists, that anything is really the way it seems ot us through our senses?

I accept no principles of physics which are not also accepted in mathematics.

Now therefore, that my mind is free from all cares, and that I have obtained for myself assured leisure in peaceful solitude, I shall apply myself seriously and freely to the general destruction of all my former opinions.

Instead I ought to be grateful to Him who never owed me anything for having been so generous to me, rather than think that He deprived me of those things or has taken away from me whatever He did not give me.

Good sense is the most equitably distributed of all things because no matter how much or little a person has, everyone feels so abundantly provided with good sense that he feels no desire for more than he already possesses.

And thereby make ourselves, as it were, the lords and masters of nature.

I was convinced that our beliefs are based much more on custom and example than on any certain knowledge.