popper-logic-scientific-discovery

probability 199
events are, or are not, determined in themselves, I shall not examine it
further here. (Cf. section 71 and 78.) If we are successful with our
prediction, we may speak of ‘laws’; otherwise we can know nothing
about the existence or non-existence of laws or of irregularities.* 2
Perhaps more worth considering than this metaphysical idea is the
following view. We encounter ‘chance’ in the objective sense, it may be
said, when our probability estimates are corroborated; just as we
encounter causal regularities when our predictions deduced from laws
are corroborated.
The definition of chance implicit in this view may not be altogether
useless, but it should be strongly emphasized that the concept so
defined is not opposed to the concept of law: it was for this reason that
I called probability sequences chance-like. In general, a sequence of
experimental results will be chance-like if the frame conditions which
define the sequence differ from the initial conditions; when the individual
experiments, carried out under identical frame conditions, will
proceed under different initial conditions, and so yield different
results. Whether there are chance-like sequences whose elements are in
no way predictable, I do not know. From the fact that a sequence is
chance-like we may not even infer that its elements are not predictable,
or that they are ‘due to chance’ in the subjective sense of insufficient
knowledge; and least of all may we infer from this fact the ‘objective’
fact that there are no laws.* 3
* 2 In this paragraph, I dismissed (because of its metaphysical character) a metaphysical
theory which I am now, in my Postscript, anxious to recommend because it seems to me to
open new vistas, to suggest the resolution of serious difficulties, and to be, perhaps, true.
Although when writing this book I was aware of holding metaphysical beliefs, and
although I even pointed out the suggestive value of metaphysical ideas for science, I was
not alive to the fact that some metaphysical doctrines were rationally arguable and, in
spite of being irrefutable, criticizable. See especially the last section of my Postscript.
* 3 It would have been clearer, I think, had I argued as follows. We can never repeat an
experiment precisely—all we can do is to keep certain conditions constant, within certain
limits. It is therefore no argument for objective fortuity, or chance, or absence of law, if
certain aspects of our results repeat themselves, while others vary irregularly; especially if
the conditions of the experiment (as in the case of spinning a penny) are designed with a
view to making conditions vary. So far, I still agree with what I have said. But there may
be other arguments for objective fortuity; and one of these, due to Alfred Landé (‘Landé’s
blade’) is highly relevant in this context. It is now discussed at length in my Postscript,
sections *90, f.