popper-logic-scientific-discovery

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new appendices
differ (if at all) from our world only with respect to the initial
conditions. 20
My position of 1949 might indeed be formulated with the help of
the following statement. Although our world may not comprise all
logically possible worlds, since worlds of another structure—with different
laws—may be logically possible, it comprises all physically possible
worlds, in the sense that all physically possible initial conditions
are realized in it—somewhere, at some time. My present view is that it
is only too obvious that this metaphysical assumption may possibly be
true—in both senses of ‘possible’—but that we are much better off
without it.
Yet once this metaphysical assumption is adopted, my older and my
present views become (except for purely terminological differences)
equivalent, as far as the status of laws is concerned. Thus my older view is,
if anything, more ‘metaphysical’ (or less ‘positivistic’) than my present
view, even though it does not make use of the word ‘necessary’ in
describing the status of laws.
(15) To a student of method who opposes the doctrine of induction
and adheres to the theory of falsification, there is not much difference
between the view that universal laws are nothing but strictly universal
statements and the view that they are ‘necessary’: in both cases, we can
only test our conjecture by attempted refutations.
To the inductivist, there is a crucial difference here: he ought to
reject the idea of ‘necessary’ laws, since these, being logically stronger,
must be even less accessible to induction than mere universal
statements.
Yet inductivists do not in fact always reason in this way. On the
contrary, some seem to think that a statement asserting that laws
of nature are necessary may somehow be used to justify
20 I call my older formulation ‘clumsy’ because it amounts to introducing the assumption
that somewhere moas have once lived, or will one day live, under ideal conditions; which
seems to me a bit far-fetched. I prefer now to replace this supposition by another—that
among the ‘models’ of our world—which are not supposed to be real, but logical
constructions as it were—there will be at least one in which moas live under ideal
conditions. And this, indeed, seems to me not only admissible, but obvious. Apart from
terminological changes, this seems to be the only change in my position, as compared
with my note in Mind of 1949. But I think that it is an important change.