An Inquiry into Meaning and Truth (1940), 1969 Pelican ed., pp. 156-157:
I will observe, however, that empiricism, as a theory of knowledge, is self-refuting. For, however it may be formulated, it must involve some general proposition about the dependence of knowledge upon experience; and any such proposition, if true, must have as a consequence that [it] itself cannot be known. While therefore, empiricism may be true, it cannot, if true, be known to be so. This, however, is a large problem.
It is indeed a large problem. But, strictly speaking, is empiricism self-refuting? A self-refuting proposition is one that entails its own falsehood. *All generalizations are false* is self-refuting in this sense. It is either true or not true (false). (Assume Bivalence) If true, then false. If false, then false. So, necessarily false. Other self-refuting propositions are antinomies: if true, then false; if false, then true.
Let empiricism be the proposition, *All knowledge derives from sense experience.* Clearly, this proposition does not refute itself. For it does not entail its own falsehood. It is not the case that if it is true, then it is false. Rather, if it is true, then it cannot be known to be true. For it is not known by experience, and therefore not knowable if true.
Empiricism, then, is not self-refuting, but self-vitiating, self-weakening. It is in this respect like the thesis of relative relativism (RR): it is relatively true that all truths are relative. (RR) does not refute itself, but it does weaken itself. Presumably, what the relativist really wants to say is something stentorian and unqualified: all truths are relative! But the demands of logical consistency force him to relativize his position.
The real problem is that if empiricism is true, then it cannot be believed with justification. For on empiricism the only justificatory grounds are those supplied by sense experience. It is also quite clear that empiricism is not a formal-logical truth or an analytic truth. A logical positivist would have to say it is cognitively meaningless. But we shouldn't go that far. It plainly enjoys cognitive meaning.
You might say that empiricism is just a linguistic proposal, a non-binding suggestion as to how we might use words. Equivalently, one might say it is just a stance one might adopt. If you tell me that, then I will thank you for 'sharing,' but then politely voice my preference for either a non-empirical stance or a stance that is not a mere stance, but the blunt asseveration that empiricism is false. After all, I know that kindness is to be preferred over cruelty, ceteris paribus, and I know this by a non-empirical value intuition.
Another wrinkle is this. If all knowledge derives from sense experience, then presumably this cannot just happen to be the case. I should think that if empiricism is true, then it is necessarily true. But what could be the ground of the necessity? I have already noted, in effect, that the necessity is neither formal-logical nor analytic. Is the necessity grounded in the nature, essence, eidos, of knowledge? That would be a rather unempirical thing to say. Empiricists have no truck with essences or Forms or eide.
Here then we appear to have a further embarrassment for empiricism. It cannot be the nature of knowledge to derive from and have its sole justificatory ground in sense experience. So it just happens to be the case. This cannot be ruled out as logically impossible. But it smacks of deep incoherence and is, shall we say, profoundly unsatisfactory.
Please note that similar reasoning can be deployed against scientism. If all knowledge is natural-scientific knowledge, then this proposition, if true, cannot be known to be true. Is it then merely believed without justification? Is it merely a matter of adopting the 'scientistic stance' or doing the 'scientistic shuffle'? If so, I will thank you for 'sharing' but then politely refuse your invitation to dance.
That puts me in mind of the old idea of John Stuart Mill and others that the laws of logic are empirical generalizations from what we do and do not perceive. Thus we never perceive rain and its absence in the same place at the same time. The temptation is to construe such logic laws as the Law of Non-Contradiction -- ~(p & ~p) -- as generalizations from psychological facts like these. If this is right, then logical laws lack the a priori character and epistemic ‘dignity’ that some of us are wont to see in them. They rest on psychological facts that might have been otherwise and that are known a posteriori.
London Ed might want consider this reductio ad absurdum:
1. The laws of logic are empirical generalizations. (Assumption for reductio) 2. Empirical generalizations, if true, are merely contingently true. (By definition of ‘empirical generalization’: empirical generalizations record what happens to be the case, but might not have been the case.) Therefore, 3. The laws of logic, if true, are merely contingently true. (From 1 and 2) 4. If proposition p is contingently true, then it is possible that p be false. (Def. of ‘contingently true.’)Therefore, 5. The laws of logic, if true, are possibly false. (From 3 and 4)Therefore, 6. LNC is possibly false: there are logically possible worlds in which ‘p&~p’ is true. (From 5 and the fact that LNC is a law of logic.) 7. But (6) is absurd (self-contradictory): it amounts to saying that it is logically possible that the very criterion of logical possibility, namely LNC, be false. Corollary: if laws of logic were empirical generalizations, we would be incapable of defining ‘empirical generalization’: this definition requires the notion of what is the case but (logically) might not have been the case.
0. Herewith, some interpretative notes on Curt Ducasse, "On the Nature and Observability of the Causal Relation," in Causation, eds. Sosa and Tooley, Oxford 1993, pp. 125-136.
1. Assuming that causality is a relation (not entirely obvious!), the question arises as to what sorts of entity can serve as its relata. Following Schopenhauer, whom he cites, Curt Ducasse holds that in strict propriety only events can be causes and effects. An event is either a change or an absence of a change. Thus a tree's losing its leaves is an event, but a tree is not. In strict propriety, it makes no sense to say that Bill was killed by a mountain lion. One has to say something like: Bill was killed by the attack of a mountain lion. In the attack the lion is the agent as Bill is the patient, but the latter is no more the effect than the former is the cause. The cause is the lion's attack, the effect is Bill's death. Some theorists distinguish between agent-causation and event-causation, but for Ducasse, there is no such thing as agent-causation: causation just is event-causation.