Perhaps there is an argument here: sum, ergo cogito. In other words, if one can apperceive (that is, if they can perceive that they perceive, for instance by perceiving that they perceive themselves), then one can conclude that one must be a thinking thing. This argument would cut deep against the criticisms advanced by Nietzsche and others that one cannot legitimately draw the conclusion that “I exist” from the fact that “I think” (or, as they might have it, that ‘thinking’ is happening). Nietzsche suggests that “I think therefore I am” is fallacious because it uses the first person instead of, say, the third person. Contra Nietzsche we should say that if I can apprehend that ‘I [first person] exist’ as self evidently true then I can also derive ‘I’ from thinking. The fact that there is thought doesn’t on it’s own entail that I exist, but the fact that there is thought combined with the fact that thought rationally obviates the first-person perspective does entail that I exist, and the first person perspective is entailed by the fact that there is thought.
Thus, if I can apprehend that ‘I am’ then it follows from that that I am an apprehending thing (that I apprehend at least one thing, which makes me a thinking thing).
Descartes’ mistake, if he made one, would be that his thinking dialectically led him to what was already a self-evident truth, but he argued for it from something which did not actually logically entail it, or at least not without the question begging assumption that “I” is doing the thinking (that thinking is occurring does not license the claim that I exist). To shore up his argument, then, we could simply add that if I apprehend that I exist then I know that I am a thinking thing. This thought might also have interesting implications for personal identity and the way humans are qualitatively different from animals.