Moore’s argument is a defense against radical skepticism of Descartes.

  1. Here is one hand.
  2. Here is another hand.

Therefore, two human hands exist at this moment. Thus, external objects exist.

Translating this reasoning by Descartes argument, we will get the following:

  1. If I know that I am sitting by the fire, then I know that I am not dreaming
  2. I know that I am sitting by the fire.

Therefore, I know that I am not dreaming.

P → Q
P
—
Q

Moore’s proof of external objects is based on empirical objects that are mapped in space and that are external to the minds. Nevertheless, sceptics can argue that we cannot know things which we cannot prove. The sceptic’s argument will be construed in the following way:

  1. If I know that I am sitting by the fire, then I know that I am not dreaming
  2. I do not know that I am sitting by the fire since I cannot prove it.

Therefore, I do not know that I am not dreaming.

P → Q
∼ Q
—
∼ P

Everything that I can actually experience I can dream that I experience. I cannot distinct a dream state and an awakened state. If sceptics say that it is logically possible to have sensory experiences and yet be dreaming, then the Moore’s argument fails. The sceptic’s argument is stronger and more theoretically interesting.

Bibliography:

  • “A defence of common sense”, published in Contemporary British Philosophy (2nd series), ed. J. H. Muirhead, 1925. Reprinted in G. E. Moore, Philosophical Papers (1959)
  • “Proof of an External World” Proceedings of the British Academy 25 (1939) 273-300. Reprinted in Philosophical Papers and in *G. E. Moore: Selected Writings 147-70.