I suppose therefore that all things I see are illusions; I believe that nothing has ever existed of everything my lying memory tells me. I think I ha… - René Descartes

I suppose therefore that all things I see are illusions; I believe that nothing has ever existed of everything my lying memory tells me. I think I have no senses. I believe that body, shape, extension, motion, location are functions. What is there then that can be taken as true? Perhaps only this one thing, that nothing at all is certain.

But I cannot forget that, at other times I have been deceived in sleep by similar illusions; and, attentively considering those cases, I perceive so clearly that there exist no certain marks by which the state of waking can ever be distinguished from sleep, that I feel greatly astonished; and in amazement I almost persuade myself that I am now dreaming.

Il est bon de savoir quelque chose des moeurs de divers peuples, afin de juger des nôtres plus sainement, et que nous ne pensions pas que tout ce qui est contre nos modes soit ridicule et contre raison, ainsi qu'on coutume de faire ceux qui n'ont rien vu.

Even if all knowledge could be found in books, where it is mixed in with so many useless things and confusingly heaped in such large volumes, it would take longer to read those books than we have to live in this life and more effort to select the useful things than to find them oneself

There is nothing more ancient than the truth.