“Cogito ergo sum. (I think, therefore I am.)”

“I doubt, therefore I think, therefore I am.”

“I think; therefore I am.”

“Dubito, ergo cogito, ergo sum.(English: "I doubt, therefore I think, therefore I am")”

“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.”

“And what more am I? I look for aid to the imagination. [But how mistakenly!] I am not that assemblage of limbs we call the human body; I am not a subtle penetrating air distributed throughout all these members; I am not a wind, a fire, a vapor, a breath or anything at all that I can image. I am supposing all these things to be nothing. Yet I find, while so doing, that I am still assured that I am a something.”

“I am thing that thinks: that is, a things that doubts,affirms, denies, understands a few things, is ignorant of many things, is willing, is unwilling, and also which imagines and has sensory perceptions.”