Hume's skepticism.

It is known to every student of philosophy that the father of skeptecism David Hume, rejected the very basis of Cartesian Cogito and replaced it with Bundle theory.He was of the view that any impression or complex idea for which there is no corresponding object in external reality must be put to flames.My objection to it is that ,Hume seems to presuppose external reality(a complex idea) because the idea of external reality is implied in sensation.

My problem with Realists have always been that they think that reality is something self-evident when it is the most hardest things to achieve.But its even more annoying that a skeptic like Hume presupposes sensations to achieve systematic conclusions.