The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself.
— Bertrand Russell
If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.
— René Descartes
There is no truth. There is only perception.
— Gustave Flaubert