Anyone who’s even heard of Popper knows that he advanced his falsifiability criterion (of science) in opposition to the Vienna Circle’s verifiability criterion (of meaning). What the Popper fans seem unaware of (yes, I know, they’re no longer as numerous as in the days of Helmut Schmidt’s public endorsement) is that Carnap actually responded to this criticism by pointing out that you can’t distinguish between verification and falsification except in certain special cases, which happen not to include the laws of e.g. physics. That was in “Testability and Meaning” (1936-7), which Popper praised volubly, e.g. in his Schilpp volume. But despite the fatal consequences of Carnap’s argument for Popper’s whole edifice, Popper never responded, nor, as far as I’m aware, has any of his followers.
I found this incredible, given the centrality of Carnap’s point to Popper’s project, so once when on the HOPOS mailing list, as occasionally used to happen, Popper came up and various Popperians complained about misconceptions about Popper, I wrote the following (apologies to the hopoi who may be reading this and are very bored with Popperiana by now):
. . . while we’re on the subject of common misperceptions about Popper: why does no one talk about Carnap’s demonstration, in “Testability and Meaning,” that for sentences of the form “for all x there exists a y such that (. . .x. . .y)” — any sentence using a limit concept, for instance, i.e. most laws of theoretical physics — falsification is essentially equivalent to verification (see Carnap Schilpp volume p. 879 for a brief summary). As far as I’m aware neither Popper himself nor any Popperian has ever acknowledged this problem or tried to figure out a way around it. Miller’s 1994 book (Critical Rationalism: A Restatement and Defence), for instance, has a section on the “asymmetry between falsification and verification,” but only rather flimsy challenges to it are acknowledged, not the comprehensive treatment of T&M. But I haven’t studied this literature thoroughly. . .
The first time I sent this, there was no response. A few months later, Popper came up again, and I re-sent the above paragraph in a slightly different context, and again asked whether anyone knew of a response to Carnap’s point. Joseph Agassi answered this time:
the reason Popper and cohorts failed to respond to Carnap’s problem is that it is a problem for Wittgenstein addicts only. Only they want sentences to be testable. In his Replies Einstein says, no one demands that every sentence in a testable theory is testable. Wittgenstein’s requirement of sentences that they “show” their truth value in order to be meaningful (i.e. to have truth value) is to be rejected, and with it the problem that you insist on.
To which I responded as follows:
No, Popper often acknowledged that it’s his problem: “My proposal is based upon an asymmetry between verifiability and falsifiability; an asymmetry which results from the logical form of universal statements. . .” (LSD p. 41). And §22 of the Postscript, entitled “The Asymmetry between Falsification and Verification,” takes 8 pages to fend off all sorts of other objections that had been raised against this asymmetry, but never the Carnap issue of nested quantifiers (which, as I remarked earlier, are indispensable to any theory whose statement involves e.g. limit concepts): “Although some of my critics have denied the existence of this asymmetry, their arguments were anticipated and fully answered in my LSD. . . This fundamental asymmetry cannot, I think, be seriously denied: a set of singular observation statements. . . may at times falsify or refute a universal law; but it cannot possibly verify a law. . . This is the fundamental logical situation; and it shows a striking asymmetry.” And so on. Popper himself thought (as in the sentence quoted from LSD above) that his entire criterion of demarcation depends on this supposed asymmetry. But when Carnap showed in T&M that “the fundamental logical situation” is a bit more complicated than that, and that verifiability and falsifiability are only distinguishable in certain special cases, not in general, Popper doesn’t even acknowledge the problem.
Nor does this have anything to do with Einstein’s issue regarding systems of sentences — that not every sentence can be testable in isolation; Popper’s requirement (like the one Carnap considers in T&M) is that some sentences should be testable. Wittgenstein did not require that sentences “show” their truth value in order to be meaningful, but in any case that has nothing to do with Popper’s acknowledgement that his criterion of demarcation is based on the asymmetry between falsification and verification or with Carnap’s pointing out that this asymmetry holds only in certain simple special cases, not for e.g. the laws of physics as we know them.
I can’t remember whether there were any further substantive responses to this; I think not, as the moderators soon shut down the discussion. That was about a year ago, I think. In any case, there was certainly no response to Carnap’s argument. So I will here repeat my question yet again: does anyone know of a response to Carnap’s argument?