René Descartes
Meditations on First Philosophy
“But what shall I say now about this supposition that some supremely powerful and – if I may be permitted to say so – malicious deceiver is deliberately trying to trick me any way he can? Can I affirm that I possess the least of all those attributes which I have just now declared to belong to the nature of a body? I examine them, reflect on them, turn them over again, but nothing comes to mind. It is tedious and pointless to run through the list again. But what about the attributes I assigned to the soul? Nutrition or locomotion? Since now I do not have a body, these are mere delusions. Sense-perception? There can be nothing of the sort without a body, surely; and besides, when asleep I have appeared to perceive through the senses many things which later I realized I did not perceive through the senses at all. Thinking? At last I have found it – thought. This alone is inseparable from me. I am, I exist – that is certain. But for how long? For as long as I am thinking. For it could be that, were I to completely cease thinking, I should completely cease to exist. At present I am not admitting anything except what is necessarily true. I am, then, in the strict sense, only a thing that thinks. That is, I am a mind, or intelligence, or intellect, or reason – words whose meaning I have failed to apprehend before now. But for all that I am a thing which is real and which truly exists. But what kind of a thing? As I have just said: a thinking thing”