Descartes, however, seems to escape the noose as far as this fallacy goes. He concludes principle I.8 with the following words: "So our knowledge of our thought is prior to, and more certain than, our knowledge of any corporeal thing; for we have already perceived it, although we are still in doubt about many other things." This statement is a clear affirmation that what he takes himself to have proved here is that, as far as he knows, he is only a thinking thing. He does not think that he has proved that he definitely is only a thinking thing. (Descartes will introduce the proof for this latter claim later in Part I of the Principles; that proof will rely on many of the conclusions that we will cover in the intervening sections).