What are the main arguments put forward by Moore in his paper “A Defence of Common Sense" to prove that there are possible propositions about the world that are known to be true with certainty ?

Moore’s Methodological Approach: The ‘Here is a Hand’ Argument

Moore’s approach is remarkably direct and seemingly simple. He doesn’t attempt to construct elaborate metaphysical systems or rely on traditional philosophical proofs. Instead, he presents what appear to be ordinary, common-sense propositions and asserts that he *knows* them to be true. The most famous example is his “Here is a hand” argument. He holds up his hand and states, “Here is one hand,” and then proceeds to argue that he knows this proposition is true. He doesn’t offer further justification; the act of demonstrating his hand *is* the proof, according to Moore.

The Nature of ‘Common Sense’ Propositions

Moore defines ‘common sense’ not as a particularly refined or intellectual faculty, but as the collection of propositions that most people readily accept as true. These are not propositions arrived at through rigorous philosophical inquiry, but rather the everyday beliefs that guide our actions and interactions with the world. Examples include:

• There exists an external world independent of our minds.
• The past has existed.
• Other people exist.
• Material things exist.

Moore argues that these propositions are not themselves in need of proof; rather, they are the basis upon which other proofs are built. To demand proof for these propositions is to fall into a vicious regress.

Arguments for the Certainty of Common Sense Propositions

1. The Impossibility of Consistent Skepticism:

Moore contends that a consistent skeptic cannot live according to their beliefs. If one truly doubted the existence of the external world, they would be unable to perform even the simplest actions, as these actions presuppose the reality of the world. He argues that the skeptic’s doubt is performative contradiction – they act as if the world exists while simultaneously claiming to doubt its existence.

2. Introspection and Direct Awareness:

Moore believes that we have direct introspective awareness of the truth of common sense propositions. He doesn’t claim this is a logical deduction, but a form of immediate, intuitive knowledge. When we perceive something, we don’t merely have a sensation; we also have a direct awareness of the external object causing that sensation. This awareness, he argues, is sufficient to establish the truth of the proposition.

3. The ‘Proof of External World’ as a Logical Point:

Moore argues that if he can demonstrate a particular proposition about the external world (like “Here is a hand”), he has, in effect, proven the existence of the external world. This is because the very act of demonstrating something requires the existence of something external to the demonstrator. He doesn’t see this as a grand metaphysical proof, but a simple logical point.

Addressing Objections and Limitations

Moore acknowledges that his arguments are vulnerable to criticism. Skeptics might argue that our introspective awareness is fallible, or that the ‘proof of external world’ is merely a circular argument. However, Moore maintains that these objections miss the point. He isn’t trying to convince skeptics through rational argument; he’s simply asserting that he *knows* certain propositions to be true, and that this knowledge is not based on any further justification. He is not attempting to *defeat* skepticism, but to bypass it by appealing to a different kind of knowledge – a direct, intuitive awareness of the world.

Furthermore, Moore’s reliance on ‘common sense’ is itself open to critique. What constitutes ‘common sense’ can vary across cultures and time periods. However, Moore argues that he is referring to the common sense of those engaged in rational discourse, not necessarily the beliefs of the average person.