Explain G.E. Moore's argument against scepticism.

G.E. Moore performs something known as the G.E. Moore shift. This is where he takes the sceptic's Modus Ponens argument: (1) If you can doubt the natural world then you cannot know anything about the natural world (P=>Q) (2) You can doubt the natural world (e.g. because of Descartes' Deamon) (P) (c) You cannot know anything about the natural world (Q) And turns it into a Modes Tollens argument (1) If you can doubt the natural world then you cannot know anything about the natural world (P=>Q) (2) You can know things about the natural world (that Moore has two hands) (~Q) (c) You can't doubt the natural world (~P)