I think; therefore I am.
I think, therefore I am.
Common sense is the most fairly distributed thing in the world, for each one thinks he is so well-endowed with it that even those who are hardest to satisfy in all other matters are not in the habit of desiring more of it than they already have.
Cogito ergo sum: I think, therefore I am.
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.