A Defence of Common Sense: are common-sense propositions more certain than any philosophical premise that would deny them?

G.E. Moore, answered from the texts and cited to the page.

The position in brief

Common-sense propositions are more certain than any philosophical premise that would deny them.1 The 1925 Defence lists a series of truisms Moore claims to know with certainty: "I have a body, which has existed continuously for many years; the earth has existed for many years past; I have at various times had many different experiences and continue to have them now; I am not the only person who has had experiences." The claim is not that we can prove these truisms; it is that they are more certain than any philosophical premise that would deny them.2345

If a philosophical argument concludes that "I do not know that I have a body," the right response is not to accept the conclusion but to reject one of the premises — since the conclusion is more incredible than any premise that could lead to it. The epistemological structure: certainty propagates from the more certain to the less certain, and the truisms of common sense are at the ceiling of certainty, while the premises of philosophical skepticism are nowhere near.

Moore acknowledged he did not claim to know HOW he knows the truisms; the analysis question (what is the analysis of "I know p"?) is harder than the truth question (do I know p?) and the 1925 essay is silent on the analysis. Wittgenstein's On Certainty (1969) extends the position: Moore's truisms function as "hinge propositions" on which our practices of doubt and certainty depend.

Sources

  1. II A DEFENCE OF COMMON SENSE In what follows I have merely tried to state, one by one, some of the most important points in which my philosophical position differs from positions which have been taken up by some other philosophers.
    II A Defence of Common Sense, pp. 32–33
  2. My first point, then, may be said to be that (2), together with all its implications, some of which I shall expressly mention, is true. (I) I begin, then, with my list of truisms, every one of which (in my own opinion) I know, with certainty, to be true. The propositions to be included in this list are the following: There exists at present a living human body, which is my body.
    II A Defence of Common Sense, p. 33
  3. The propositions to be included in this list are the following: There exists at present a living human body, which is my body. This body was born at a certain time in the past, and has existed continuously ever since, though not without undergoing changes; it was, for instance, much smaller when it was born, and for some time afterwards, than it is now.
    Chapter 7: A Defence of Common Sense, pp. 107–108
  4. This truism also (in my own opinion) I know, with certainty, to be true; and it is as follows: In the case of very many (I do not say all) of the human beings belonging to the class (which includes myself) defined in the following way, i.e., as human beings who have had human bodies, that were born and lived for some time upon the earth, and who have, during the lifetime of those bodies, had many different…
    Chapter 7: A Defence of Common Sense, pp. 108–109
  5. Mine is that I do know of the existence of this pencil; unless this premiss not only is true, but is absolutely known to be so, my argument to prove that Hume's principles are false cannot be conclusive. And moreover the degree of certainty of the conclusion, in either case, supposing neither is quite certain, will be in proportion to the degree of certainty of the premiss.
    Some Main Problems of Philosophy, pp. 133–134

Where the argument is made

  • 'A Defence of Common Sense' (1925, in Philosophical Papers 1959 and Selected Writings)
  • Some Main Problems of Philosophy (1953 posthumous, lectures from 1910-11) on common-sense and philosophical doubt
  • 'Four Forms of Scepticism' (in Philosophical Papers)
  • 'Certainty' (in Philosophical Papers, in Selected Writings)

How the argument was received

The Defence of Common Sense is one of the central texts of twentieth-century anti-skeptical epistemology. Wittgenstein's On Certainty (1969) is the major extension and modification. Stroud's The Significance of Philosophical Skepticism (1984) is the central post-war engagement, arguing the Moorean response fails to engage the skeptic's actual concern. Contemporary Mooreans (Pryor, Wright, Coliva) defend modified versions; the dogmatist-vs-conservativist debate runs through the contemporary epistemology literature. The position remains contested but live.