There are plenty of things of which there is clearly no doubt, although it is from the senses that we learned them: for instance, that I am now here, sitting by the fire, wrapped in a warm winter gown, handling this paper, and suchlike. Indeed, that these hands themselves, and this whole body are mine — what reason could there be for doubting this?
I will suppose that, not God, who is perfectly good and the source of truth, but some evil spirit, supremely powerful and cunning, has devoted all his efforts to deceiving me, I will think that the sky, the air, the earth, colours, shapes, sounds, and all external things are no different from the illusions of our dreams, and that they are traps laid for my credulity; I will consider myself as having no hands, no eyes, no flesh, no blood, and no senses; but yet as falsely believing that I have all of these.
Yesterday’s meditation has plunged me into so many doubts that I still cannot put them out of my mind, nor, on the other hand, can I see any way to resolve them; but, as if I had suddenly slipped into a deep whirlpool, I am in such difficulties that I can neither touch bottom with my foot nor swim back to the surface.
But indeed I do not yet sufficiently understand what this ‘I’ is that now necessarily exists; so that from now on I must take care in case I should happen imprudently take soemthing else to be me that is not me, and thus go astray in the very knowledge that I claim to be the most certain and evident of all … What about thinking? Here I do find something: it is thought; this alone cannot be stripped from me. I am, I exist, that is certain. But for how long? Certainly only for as long as I am thinking; for perhaps if I were to cease from all thinking it might also come to pass that I might immediately cease altogether to exist.
What you can’t see is that at one point the cloud was a peculiar greenish color, and there’s a little cloud in front that’s cotton candy blue. Not the sky, mark you, but the cloud. Perhaps if Descartes had spent less time on geometry and more looking at the sky from somewhere in the Southwest desert he would have been less doubtful about the reality of physical existence. But then again, perhaps not.