on the cogito, the thinking thing

Having carried out his radical doubting of everything, Descartes seeks out one point which may be seen as being certain.

"I shall proceed by setting aside all that in which the least doubt could be supposed to exist. I suppose, then, that all the things that I see are false; I persuade myself that nothing has ever existed of all that my fallacious memory represents to me. I consider that I possess no senses; I imagine that body, figure, extension, movement and place are but the fictions of my mind. What then can be esteemed as true? I was persuaded that there was nothing in all the world. Was I not then likewise persuaded that I did not exist? Not at all; of a surety I myself did exist because I persuaded myself of something. But [if] there is some deceiver or other, very powerful and very cunning, who ever employs his ingenuity in deceiving me, then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think I am something. I am, I exist, is necessarily true each time I pronounce it, or that I mentally conceive it."

What attributes can Descartes have without requiring a body in which he can have no certainty? Obviously not any of the movements or sensations of bodies, but

"What of thinking? I find here that thought is an attribute that belongs to me; it alone cannot be separated from me. I am, I exist, that is certain. But what [kind of] thing [am I]?...a thing which thinks."

But what of these other 'uncertain' things? Bodies and sensations and the like.

"...solely by the faculty of judgement which rests in my mind, [do] I comprehend that which I believed I saw with my eyes. [Whatever] error may still be found in my judgement, I can nevertheless not perceive it thus without a human mind. Bodies are not, properly speaking, known by the senses or by the faculty of imagination, but by the understanding only, and since they are not known from the fact that they are seen or touched, but only because they are understood, I see clearly that there is nothing which is easier for me to know than my mind." Descartes: Meditations on the First Philosophy.