popper-logic-scientific-discovery

appendix *i 315
statement turns out not to be so reducible, then it is ‘meaningless’
or ‘nonsensical’ or ‘metaphysical’ or a ‘pseudo-proposition’. Thus
metaphysics is meaningless nonsense.
It may appear as if the positivists, by drawing this line of demarcation,
had succeeded in annihilating metaphysics more completely than
the older anti-metaphysicists. However, it is not only metaphysics
which is annihilated by these methods, but natural science as well. For
the laws of nature are no more reducible to observation statements
than metaphysical utterances. (Remember the problem of induction!)
They would seem, if Wittgenstein’s criterion of meaning is applied
consistently, to be ‘meaningless pseudo-propositions’, and consequently
to be ‘metaphysical’. Thus this attempt to draw a line of
demarcation collapses.
The dogma of meaning or sense, and the pseudo-problems to which
it has given rise, can be eliminated if we adopt, as our criterion of
demarcation, the criterion of falsifiability, i.e. of an (at least) unilateral or
asymmetrical or one-sided decidability. According to this criterion,
statements, or systems of statements, convey information about the
empirical world only if they are capable of clashing with experience; or
more precisely, only if they can be systematically tested, that is to say, if
they can be subjected (in accordance with a ‘methodological
decision’) to tests which might result in their refutation. 3
In this way, the recognition of unilaterally decidable statements
allows us to solve not only the problem of induction (note that there is
only one type of argument which proceeds in an inductive direction:
the deductive modus tollens), but also the more fundamental problem of
demarcation, a problem which has given rise to almost all the other
problems of epistemology. For our criterion of falsifiability distinguishes
with sufficient precision the theoretical systems of the
empirical sciences from those of metaphysics (and from conventionalist
and tautological systems), without asserting the meaninglessness of
metaphysics (which from a historical point of view can be seen to
3 This testing procedure is reported by Carnap in Erkenntnis 3, pp. 223 ff., ‘procedure B’.—
See also Dubislav, Die Definition, 3rd edition, pp. 100 ff.*Added 1957: This reference will be
found not to be one to Carnap’s but to some of my own work which Carnap reported
and accepted in the article referred to. Carnap made full acknowledgment of the fact that
I was the author of what he there described as ‘procedure B’ (‘Verfahren B’).