popper-logic-scientific-discovery

APPENDIX *x
Universals, Dispositions, and
Natural or Physical Necessity
(1) The fundamental doctrine which underlies all theories of induction
is the doctrine of the primacy of repetitions. Keeping Hume’s attitude in
mind, we may distinguish two variants of this doctrine. The first
(which Hume criticized) may be called the doctrine of the logical
primacy of repetitions. According to this doctrine, repeated instances
furnish a kind of justification for the acceptance of a universal law. (The
idea of repetition is linked, as a rule, with that of probability.) The
second (which Hume upheld) may be called the doctrine of the temporal
(and psychological) primacy of repetitions. According to this
second doctrine, repetitions, even though they should fail to furnish
and kind of justification for a universal law and for the expectations and
beliefs which it entails, nevertheless induce and arouse these expectations
and beliefs in us, as a matter of fact—however little ‘justified’ or
‘rational’ this fact (or these beliefs) may be.
Both variants of this doctrine of the primacy of repetitions, the
stronger doctrine of their logical primacy and the weaker doctrine of
their temporal (or causal or psychological) primacy, are untenable.
This may be shown with the help of two entirely different arguments.
My first argument against the primacy of repetitions is the following.
All the repetitions which we experience are approximate repetitions; and by