The Fabric of Reality David Deutch

7 
A Conversation About Justification
 
(or ‘David and the Crypto-inductivist’)
 
I think that I have solved a major philosophical problem: the problem of
induction.
Karl Popper
As I explained in the Preface, this book is not primarily a defence of the
fundamental theories of the four main strands; it is an investigation of what
those theories say, and what sort of reality they describe. That is why I do
not address opposing theories in any depth. However, there is one opposing
theory — namely, common sense — which reason requires me to refute in
detail wherever it seems to conflict with what I am asserting. Hence in
Chapter 2 I presented a root-and-branch refutation of the common-sense
idea that there is only one universe. In Chapter 11 I shall do the same for the
common-sense idea that time ‘flows’, or that our consciousness ‘moves’
through time. In Chapter 3 I criticized inductivism, the common-sense idea
that we form theories about the physical world by generalizing the results of
observations, and that we justify our theories by repeating those
observations. I explained that inductive generalization from observations is
impossible, and that inductive justification is invalid. I explained that
inductivism rests upon a mistaken idea of science as seeking predictions on
the basis of observations, rather than as seeking explanations in response to
problems. I also explained (following Popper) how science does make
progress, by conjecturing new explanations and then choosing between the
best ones by experiment. All this is largely accepted by scientists and
philosophers of science. What is not accepted by most philosophers is that
this process is 
justified. Let me explain.
Science seeks better explanations. A scientific explanation accounts for our
observations by postulating something about what reality is like and how it
works. We deem an explanation to be better if it leaves fewer loose ends
(such as entities whose properties are themselves unexplained), requires
fewer and simpler postulates, is more general, meshes more easily with
good explanations in other fields and so on. But why should a better
explanation be what we always assume it to be in practice, namely the token
of a 
truer theory? Why, for that matter, should a downright bad explanation
(one that has none of the above attributes, say) necessarily be false? There
is indeed no logically necessary connection between truth and explanatory
power. A bad explanation (such as solipsism) 
may be true. Even the best
and truest available theory may make a false prediction in particular cases,
and those might be the very cases in which we rely on the theory. No valid
form of reasoning can logically rule out such possibilities, or even prove
them unlikely. But in that case, what justifies our relying on our best
explanations as guides to practical decision-making? More generally,
whatever criteria we used to judge scientific theories, how could the fact that
a theory satisfied those criteria today possibly imply anything about what will
happen if we rely on the theory tomorrow?
This is the modern form of the ‘problem of induction’. Most philosophers are
now content with Popper’s contention that new theories are not inferred from

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anything, but are merely hypotheses. They also accept that scientific
progress is made through conjectures and refutations (as described in
Chapter 3), and that theories are accepted when all their rivals are refuted,
and not by virtue of numerous confirming instances. They accept that the
knowledge obtained in this way tends, in the event, to be reliable. The
problem is that they do not see why it should be. Traditional inductivists tried
to formulate a ‘principle of induction’, which said that confirming instances
made a theory more likely, or that ‘the future will resemble the past’, or some
such statement. They also tried to formulate an inductive scientific
methodology, laying down rules for what sort of inferences one could validly
draw from ‘data’. They all failed, for the reasons I have explained. But even if
they had succeeded, in the sense of constructing a scheme that could be
followed successfully to create scientific knowledge, this would not have
solved the problem of induction as it is nowadays understood. For in that
case ‘induction’ would simply be another possible way of choosing theories,
and the problem would remain of 
why those theories should be a reliable
basis for action. In other words, philosophers who worry about this ‘problem
of induction’ are not inductivists in the old-fashioned sense. They do not try
to obtain or justify any theories inductively. They do not expect the sky to fall
in, but they do not know how to justify that expectation.
Philosophers today yearn for this missing justification. They no longer
believe that induction would provide it, yet they have an induction-shaped
gap in their scheme of things, just as religious people who have lost their
faith suffer from a ‘God-shaped gap’ in 
their scheme of things. But in my
opinion there is little difference between having an X-shaped gap in one’s
scheme of things and believing in X. Hence to fit in with the more
sophisticated conception of the problem of induction, I wish to redefine the
term ‘inductivist’ to mean someone who believes that the 
invalidity of
inductive justification is a problem for the foundations of science. In other
words, an inductivist believes that there is a gap which must be filled, if not
by a principle of induction then by something else. Some inductivists do not
mind being so designated. Others do, so I shall call them 
crypto-inductivists.
Most contemporary philosophers are crypto-inductivists. What makes
matters worse is that (like many scientists) they grossly underrate the role of
explanation in the scientific process. So do most Popperian anti-inductivists,
who are thereby led to deny that there is any such thing as justification (even
tentative justification). This opens up a new explanatory gap in 
their scheme
of things. The philosopher John Worrall has dramatized the problem as he
sees it in an imaginary dialogue between Popper and several other
philosophers, entitled ‘Why Both Popper and Watkins Fail to Solve the
Problem of Induction’.[1] The setting is the top of the Eiffel Tower. One of the