[lit-ideas] Popper on Ayer

  • From: Donal McEvoy <donalmcevoyuk@xxxxxxxxxxx>
  • To: lit-ideas@xxxxxxxxxxxxx
  • Date: Wed, 28 Jul 2010 15:49:29 -0700 (PDT)

From P's _Schilpp_ Vol.II, p.1105-7, replying to Ayer on _The Verification of 
Theories_ :-

<"First, however," Ayer writes...,"I want to examine his [Popper's] claim that, 
at any rate so far as empirical propositions are concerned, there are no 
general criteria by which we can recognise truth." Thus it is my claim which is 
examined here, and the term "criterion of truth" is clearly used in the sense 
explained [above] - a general criterion by which we can recognise truth.
    Yet after a number of remarks in which he seems to agree with me (as well 
as a few pinpricks along the way), Ayer reaches at the end...a conclusion which 
is the precise opposite of mine:
     "Accordingly, if we can lay down a general criterion for recognising the 
truth of basic statements [test statements], there is a sense in which we shall 
after all have a general criteron for recognising empirical truth."
     By "empirical truth" Ayer means, especially, the truth of scientific 
theories; and...[he] implies that, given an empirical method to decide on the 
truth or falsity of what I in _LdF_ called "basic statements" (and now prefer 
to call "test statements"), we can decide the truth or falsity of scientific 
     It may be said that Ayer does not and cannot mean this, because...he 
himself repeats most of the arguments by which I support my thesis of the 
one-sided refutability of universal theories. However, [he does mean this, and 
supports it with]...an apparently smooth-running but quite invalid argument...
     Ayer's argument is, in brief:
     Step (1) Admission: "Finding a counterexample proves the statement false, 
but failing to find one does not prove it true..."
     Step (2) "Nevertheless...the absence of any counterexample...is...a 
necessary and sufficient condition of truth...." [This step is invalid, as I 
shall show, and it invalidates the argument; but even if we grant it, the 
argument does not become valid.]
     Step (3) "...the only way in which an empirical statement can meet with a 
counterexample is by its coming into conflict with a basic statement [test 
statement]...[; thus] the truth or falsity of any empirical statement...is 
entirely determined by the truth or falsity of _some set_ of basic statements." 
(Italics mine.)*
     Step (4) consists of the..statement..as quoted above, "...we shall after 
all have a general criterion for recognising empirical truth."
      Is the argument valid, provided we admit step (2), as for the moment I am 
prepared to do? If it sounds so, it is because Ayer is a trifle indistinct 
about what set of basic statements is "some set of basic statements". For the 
set of basic statements actually necessary to "determine" the truth of a theory 
_A_ would be the infinite _set of all test statements_ which could be _relevant 
to A_, reporting on all possible tests undertaken _anywhere in the universe, in 
the past, present, or future_.
      This is obvious; for by Ayer's own admission (see step (1) above), 
"failing to find [a counterexample]...does not prove...[the theory] true", 
_because_ there may be unrecorded counterexamples. Thus only if that 
questionable set of basic statements includes complete reports about all 
possible counterexamples could the set "determine" the truth of the theory _A_ 
(always provided we grant step (2)...), while _one_ counterexample, _one_ test 
statement, could determine the falsity of _A_.
      But if this set of basic statements is infinite - one might even say 
"indefinite" - it is clear that we would need more than "a general criterion 
for recognising the truth of basic statements" in order to obtain a "general 
criterion for recognising empirical truth"; in just the same way, and for just 
the same reason, that we need more than a "criterion" for recognising the 
whiteness of swans in order to determine whether _all_ swans are white...To 
"recognise" the truth of all the basic statements belonging to the set is 
clearly not an empirical process: it would involve a kind of omniscience - an 
omniscience with respect to basic statements.
      Thus Ayer's argument establishes at best merely the thesis: "basic 
omniscience" (as I will call it) is involved in any "general criterion for 
recognising empirical truth"; or _empirical omniscience involves basic 
       This thesis...even if it were validly argued...would not reveal any 
weakness in my views.
      But even this somewhat unexciting thesis is invalid, owing to the 
invalidity of Ayer's step (2)...
      Ayer contends that "the absence of any counterexample is a necessary and 
sufficient condition of truth". This view may be defended for theories like 
"All swans are white": if there exists (existed, will exist) no counterexample, 
that is, no non-white swan, then indeed the theory is true. But the view is 
untenable for all more abstract theories, such as Newton's. Non-white swans are 
observable. Newton's forces varying inversely with the square of the distance 
are not...The idea that two theories which agree with respect to all testable 
consequences must be equivalent, is mistaken. Einstein's special theory of 
relativity and Lorentz's interpretation of it are two theories which contradict 
each other (Lorentz suggested the existence of an inertial system that is 
absolutely at rest). It does not help here to say that Lorentz's interpretation 
contains a metaphysical element that _has_ to be omitted: Einstein's denial is 
just as metaphysical, or almost
 as metaphysical, because nothing observable follows from it...
       But if _A_ and _B_ are incompatible, they cannot both be true, even if 
there is no counterexample to either of them; and this means that Ayer's 
suggestion (2), that the absence of counterexamples is a sufficient condition 
for the truth of a theory is mistaken.>

Using P's own words rather than perspectivising
* From the "Dictionary of Philosophy":- "Italics: Always "mine" unless "added". 
See _Emphasis_.


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