[The metaphorical jump.]
The Metaphysical Presupposition: A Sleight of Hand(s)
Wittgenstein responds to the challenge posed most strongly by Descartes’ Meditations: having been deceived in the past, how is it that humans can know anything for certain, secure objective knowledge? In order for philosophy and science to proceed assuredly, it seems as if this challenge must be satisfied—Cartesian knowledge must be grounded on something unmoving. Descartes characterizes knowledge itself, the cogito, as in a sense securing for itself objectivity. The Cartesian-rational God is concomitant with the cogito. If there is a God who isn’t a deceiver, then humans can know things with certainty. Descartes’ metaphysical presupposition is that there is a rational God; this God is both grounded by and grounds the very possibility of objective knowledge, and this ground falls before all empirical experience. By supposing the existence of God, humans have certainty, and therefore knowledge. The notion of an undeceiving God grounds the epistemological criterion of seeing a proposition in a clear and distinct light.
But rather than address in On Certainty philosophy’s seduction by metaphysics, Wittgenstein builds upon another philosopher’s response to this question about transcendental certainty. And ironically, he finds a metaphysical presupposition in a most unlikely place, G. E. Moore’s supposedly commonsensical attempt to prove the existence of an external world.[i] In his attempt, Moore conceals a metaphysical presupposition when he says, “I certainly did at the moment know that which I expressed,” by holding up two hands.[ii] His presupposition is that he can say meaningfully, and with certainty, the he knows a proposition of the type “I have two hands.” Wittgenstein’s criticism is not that such knowledge is impossible, but rather that an utterance like “I know I have two hands” is probably nonsense. That is, Moore presupposes that he can merely, meaningfully say, “I know I have two hands.”
When philosophers use “I know…” Wittgenstein says, “I want to reply ‘you don’t know anything!’—and yet I would not say that to anyone who was speaking without philosophical intention.”[iii] The asymmetric response to different utterances of “I know…” gives a demonstration of Wittgenstein’s notion of knowledge and its attendant utterances: the meaning of such an utterance is heavily dependent on a context, and the sense or meaning of the utterance “I know…” depends on the context in which it is used. Moore’s use of “I know I have two hands” lacks an appropriate context. It is not that Moore’s utterance cannot make sense, but he makes an uncalled for assumption that it makes sense and expresses a certainty. It rests therefore on the same type of metaphysical presupposition that Descartes makes in his Meditations. That is, a common understanding between Moore and his audience is presupposed in the same way in which Descartes roughly assumes the existence of an undeceiving God, which is the condition of meaningful intersubjective experiences. For Moore to say meaningfully “I know I have two hands” conceals a presupposition that his utterance makes sense and that that which he expresses calls for a proposition of the form “I know…”
Wittgenstein’s response is that Moore’s utterance lacks a context within which it would make sense; and Moore’s thinking that it does make sense—that it does certainly make sense—presupposes a transcendent sense of meaning that must be “further back” from the beginning. For Moore’s utterance “I know I have two hands” to make sense it must be nested within a situation from which its sense is given. Sense is conferred by context; a system of signs, actions, trainings, customs, and traditions must always already be in place in order for an utterance to make sense. Moore makes this proposition within the context of a piece of philosophy that takes up our certain knowledge of the external world. It is clear what Moore means to say: namely, he knows that there exist things in the world, for example his two hands. But Moore has gone astray. Wittgenstein isn’t prescribing a certain normal usage of the proposition “I know I have two hands.” He merely notes that in order for such a proposition to make sense it must make sense. This point is an indictment of philosophy as a whole, of what we’d call “philosophic usage,” which often fails to make sense. For Wittgenstein would rather “like to reserve the expression ‘I know’ for the cases in which it used in normal linguistic exchange.”[iv] We would like to show, then, what it is that separates “philosophic usage” from “normal usage.” Wittgenstein’s strategic work on knowledge and certainty centers around the ways in which we use propositions that express knowledge and certainty.
[i] G. E. Moore, “Proof of an External World,” in Philosophic Papers (London: George Allen & Unwin Ltd., 1959), 127-150; G. E. Moore, “A Defence of Common Sense,” in Philosophic Papers (London: George Allen & Unwin Ltd., 1959), 32-59.
[ii] Moore, “Proof,” 146.
[iii] On Certainty, §407.
[iv] On Certainty, §260.