Limitation of Doubt

Source

In the previous post was mentioned the famous dictum of a skeptical philosopher 'who forgot to mention the right consequence' of the word 'therefore' in his dictum, and what that original quote of Descartes proves is what Nasr states as:

You can negate everything, doubt everything, but you cannot doubt the instrument by which you are doubting (everything else).

Nasr also goes on to mention the "hanging man" of great Persian philosopher Ibn-e-Sina which not only explains the dilemma of men 'bend on denying the Truth', but also the great difficulty they face in rejecting practically everything (which is simply impossible): "Ibn-e-Sina talks of a hanging man, who is hung in the middle of space. His feet don't touch anything; his legs don't touch anything. He doesn't know where he is. [Thus] he can doubt the existence of earth, he can doubt the existence of air - there is nothing he cannot doubt! The one [and only] thing he cannot doubt is himself that is doubting everything."