Let whoever can do so deceive me, he will never bring it about that I am nothing, so long as I continue to think I am something.

Science is practical philosophy.

The reading of all good books is like a conversation with the finest minds of past centuries.

Everything is self-evident.

To live without philosophizing is in truth the same as keeping the eyes closed without attempting to open them.

Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency.

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