popper-logic-scientific-discovery

appendix *x 461
situation created by the inherent difficulties of inductivism or
positivism or operationalism or phenomenalism.
The phenomenalist, for instance, wishes to translate statements
about physical objects into statements about observations. For example,
‘There is a flower-pot on the window sill’ should be translatable into
something like ‘If anybody in an appropriate place looks in the
appropriate direction, he will see what he has learned to call a flowerpot’.
The simplest objection (but by no means the most important
one) to regarding the second statement as a translation of the first is to
point out that while the second will be (vacuously) true when nobody
is looking at the window sill, it would be absurd to say that whenever
nobody is looking at some window sill, there must be a flower-pot on
it. The phenomenalist is tempted to reply to this that the argument
depends on the truth-table definition of the conditional (or of
‘material implication’), and that we have to realize the need for a
different interpretation of the conditional—a modal interpretation
which makes allowance for the fact that what we mean is something
like ‘If anybody looks, or if anybody were looking, then he will see, or
would see, a flower-pot’. 25
One might think that our a→ N b could provide the desired modal
conditional, and in a way it does do this. Indeed, it does it as well as
one can possibly expect. Nevertheless, our original objection stands,
because we know that if ā is necessary—that is, if ā εN—then a→ N b
holds for every b. This means that, if for some reason or other the place
where a flower-pot is (or is not) situated is such that it is physically
impossible for anybody to look at it, then ‘If anybody looks, or if anybody
were looking, at that place, then he will, or would, see a flower-pot’
will be true, merely because nobody can look at it. 26 But this means that
25 It was R. B. Braithwaite who replied along similar lines as these to my objection
of vacuous satisfaction after a paper he read on phenomenalism in Professor Susan
Stebbing’s seminar, in the spring of 1936. It was the first time that I heard, in a context
like this, of what is nowadays called a ‘subjunctive conditional’. For a criticism of
phenomenalist ‘reduction programmes’, see note 4 and text, above.
26 A somewhat fuller statement of this view of subjunctive conditionals may be found in
my note ‘On Subjunctive Conditionals with Impossible Antecedents’, Mind N.S. 68, 1959,
pp. 518–520.