29. In the first two of his Meditations, Descartes considers the possibility that all of his beliefs are false. First, how do (a) illusions, (b) hallucinations, and (c) dreams sometimes bring about false beliefs in us? Next, even if Descartes can somehow rule out the possibility that he is dreaming, what further, more troublesome, possibility would he have to rule out in order to be confident in even such apparently obvious beliefs as that he has a pair of hands? Next, Descartes argues that even if he cannot rule out this more troublesome possibility, there is another proposition about which he cannot be mistaken. What is this other proposition about which he believes he cannot be mistaken, and how does he show that he cannot be mistaken about it?