Descartes describes his method in the meditations as one of doubting his sensations and inherited ideas until he gets to something certain: his own existence as a thinking thing. hume, on the other hand, doubts conceptual abstractions that lack a basis in sensory impressions; thus, he deems the "self" nothing more than a "bundle of perceptions" to which we attach "i think." how do these two philosophers differently employ skepticism in their arguments?