Final answer:
Moore's argument in the external world debate is based on justified belief in his two hands, using modus tollens. Philosophers have differing opinions on the validity of Moore's argument and the skeptical hypothesis.
Step-by-step explanation:
While many philosophers remain unconvinced by Moore's argument, his claim that he has two hands is based on the concept of justified belief in propositions about the external world.
Moore's argument takes the form of what is known as modus tollens, where the consequence of a conditional is denied.
In contrast, the skeptic's argument takes the form of modus ponens, where the antecedent of a conditional is affirmed.
Moore believes that he is justified in believing that he has two hands because he is able to see and feel them, which provides evidence for his belief.
He argues that he has better reason to believe in his two hands than to believe in the skeptical hypothesis, which suggests that his belief might be wrong.
However, philosophers who accept the possibility of the skeptical hypothesis disagree with Moore's premises.
Overall, Moore's argument and the skeptic's argument present different approaches to understanding justified belief in the external world, and philosophers have different perspectives on the validity of these arguments.