popper-logic-scientific-discovery

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new appendices
more abstract. There are layers of higher and higher degrees of universality,
and thus of transcendence. (In section *15 of the Postscript, an
attempt is made to explain the sense in which these are also layers of
what may be called ‘depth’.)
It is of course because of this transcendence that scientific laws or
theories are non-verifiable, and that testability or refutability is the only
thing that distinguishes them, in general, from metaphysical theories.
If it is asked why we use these transcendent universal laws instead of
keeping more closely to ‘experience’, two kinds of answer may be
given.
(a) Because we need them: because there is no such thing as
‘pure experience’, but only experience interpreted in the light of
expectations or theories which are ‘transcendent’.
(b) Because a theorist is a man who wishes to explain experiences, and
because explanation involves the use of explanatory hypotheses which
(in order to be independently testable; see section *15 of the Postscript)
must transcend what we hope to explain.
The reason given under (a) is a pragmatic or instrumentalist one,
and although I believe that it is true, I do not think that it is comparable
in importance with the reason given under (b); for even if a programme
of eliminating explanatory theories for practical purposes
(say, for prediction) were to succeed, the aim of the theorist would be
unaffected. 4
4 That it is possible to do without theories is asserted by Carnap, Logical Foundations of
Probability, pp. 574 f. Yet there is no reason whatever for the belief that Carnap’s analysis,
even if it were otherwise defensible, could be legitimately transferred from his model
language to ‘the language of science’; see my Preface, 1958. In two very interesting articles
W. Craig has discussed certain reduction programmes. (See Journal of Symb. Logic 18, 1953,
pp. 30 f., and Philosophical Review 65, 1956, pp. 38 ff.) To his own excellent critical comments
on his method of eliminating ‘auxiliary’ (or ‘transcendent’) ideas, the following
might be added. (i) He achieves the elimination of explanatory theories, essentially, by
promoting infinitely many theorems to the rank of axioms (or by replacing the definition
of ‘theorem’ by a new definition of ‘axiom’ which is co-extensive with it as far as
the ‘purified’ sub-language goes). (ii) In the actual construction of the purified system,
he is of course guided by our knowledge of the theories to be eliminated. (iii) The purified system
is no longer an explanatory system, and no longer testable in the sense in which
explanatory systems may be testable whose testability is, essentially, related to their