PRAGAMATIC INDUCTION
Popper’s views on induction are more an
evasion of Hume’s problem than a solution
to it.
But the fact of the matter is we need to
make decisions about how to act.
 Life would otherwise come to a standstill
In order to do this, however, we need to
make predictions about what will occur.
If, as Popper argues, science doesn’t do
this, how can we make rational decision
about courses of action to take?
 Also, is it true that science never aims to
make predictions? We shall discuss this
question as well.
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Falsification and prediction
Does Popper’s falsification program offer us
any clues as to how to make rational
predictions?
Well, it does offer one negative suggestion:
Don’t base predictions on falsified
hypotheses.
 E.g., avoid F = 2ma3
This seems reasonable enough: if a true
conclusion is desired, don’t reason on the
basis of false premises.
 So we must choose theories that
haven’t been refuted.
But this isn’t much. In fact, if this is all we
have to go on, we have a problem…
2
Infinitely many hypotheses
We have only carried out finitely many tests.
But there are infinitely many hypotheses.
 So, as Salmon points out, infinitely
many hypotheses haven’t been ruled
out.
 Remember, on Popper’s view neither F
= ma nor E = mc2 has been confirmed or
shown to be true.
So, are we simply free to choose amongst
them?
 But some will give predictions that
conflict with those given by others.
There appears to be no rational basis for
preference when choosing hypothesis to
help one make predictions.
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Corroboration and prediction
It is worth noting that on Popper’s view
corroboration has no predictive power.
 It is nothing more than an appraisal of a
theory’s performance in the past.
A corroborated theory is simply a theory that
hasn’t yet been falsified.
To make this claim is not, Popper insists, to
suggest that the theory will perform well in
the future.
Why not? The answer is that to do so
would be to engage in inductive reasoning:
theory T has performed well in the past so it
will perform well in the future.
 As we have seen, Popper attempts to
purge such reasoning from science.
 Science is not in the prediction
business, on his view.
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Import vs. content
An important distinction:
Corroboration has no predictive import.
 This means that the very fact that a
theory is corroborated has no bearing
on whether it will continue to be.
Theories have predictive content.
 Many scientific hypotheses are universal
generalizations, i.e. they cover events at
all times and places.
 So, these theories do say something
about the future.
 So, reasoning on the basis of a theory
will provide a guide to action.
The question is whether there can be a
reason to prefer one theory over another
 This is a question about justification for
a theory, not content of a theory.
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Theoretical vs. practical rationality
When it comes to reasoning, Popper
distinguishes theoretical from practical
concerns.
 The scientist is interested in coming up
with good theories, i.e. theories that lead
to many tests.
 Those that survive the tests are kept for
further testing
 That is surely the rational thing to do:
discard falsified theories and keep going
with corroborated ones.
This is theoretical rationality and it contains
absolutely no presumption that a hypothesis
is more likely to survive tomorrow because it
survived yesterday.
So what is one to do when reasoning about
action?
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A tension
Popper claims, curiously, that we should
use corroboration when choosing
hypotheses on which to base predictions:
…we should prefer the best tested theory as a basis
for action…since we have to chose, it will be ‘rational’
to choose the best tested theory. (p. 440)
This is a curious combination.
 On the one hand, the fact that a theory
is highly corroborated says nothing
about its future performance.
 On the other, when one must reason
about the future, it is rational to pick the
most corroborated theory.
But how can corroboration lend any
justification to the choice?
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The problem
How can it be rational to base a prediction
on a theory in virtue of something that has
no implications whatsoever for predictive
power?
Analogy: We compare two theories, T1 and
T2.
 Both are corroborated.
 T1 has more vowels than T2.
We insist: the number of vowels in a theory
has no bearing at all on how the theory will
perform in the future (seems reasonable).
 But, suppose we also say: if you have to
pick one for prediction, pick T1 because,
after all, it has more vowels.
This is hardly persuasive given the first
point.
 Popper’s view faces a similar
predicament, according to Salmon.
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Circularity
Suppose S must act and H1 and H2 are the
relevant hypothesis to choose from.
Suppose H1 is corroborated but not H2.
 Isn’t it rational to pick H1?
 Watkins: S has nothing else to go on!
Salmon: that simply begs the question.
 There is plenty more to go on: S could
count vowels, toss a coin, consult a
horoscope, etc.
 The point must be that there is nothing
else to go on that is rational.
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Problems with this reply
Note: this response assumes that basing
prediction on corroboration is rational.
But this is circular reasoning, because the
question under consideration is whether
such a choice is rational.
 After all, perhaps no choice is rational
(Hume’s conclusion). So even if S had
nothing more to go on, it wouldn’t follow
that such reasoning is rational.
 Finally, hasn’t Popper insisted all along
that corroboration has no predictive
import? So how can the choice be any
more rational than flipping a coin?
10
Vindication
Recall the import/content distinction.
 Let P = theory T is well corroborated.
According to Popper, P has neither
predictive content nor predictive import:
 It has no predictive content because it
says nothing about future behaviour.
 It has no import because it cannot
provide justification for assuming T will
continue to be corroborated. If it did,
this would be inductive reasoning.
Salmon: but how can we reconcile the
second point with the directive to choose
the corroborated theory when making
predictions?
 That directive has predictive import: it is
supposed to rationally justify a choice.
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Upshot
In sum, Salmon’s criticism is that it is
implausible to suppose both
1. That corroboration statements have no
predictive import
2. That the directive to choose the most
corroborated theory when making
predictions is rationally grounded.
Anti-inductivists need some way to vindicate
(2) in light of (1).
Until then, they have no way of arguing that
some predictions are more rational than
others.
 You might as well use astrology as
astronomy; palm reading as physics.
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Inductive logic
How might the directive to choose
corroborated theories be vindicated?
 The most plausible suggestion is that
corroboration has predictive import after
all.
 In other words, rational decision making
relies on induction.
 So the project of purging induction from
human reasoning appears unlikely to
succeed.
But, can theoretical science proceed without
induction?
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Theoretical prediction
Salmon: Popper’s program appears to fail
as an account of practical action; but it also
an impoverished understanding of science.
 There is no reason to think that
scientists only wish to make bold
conjectures then criticize them.
Many scientific predictions are made for
theoretical or practical purposes e.g.:
1. Will this nuclear chain reaction come
to a (natural) close?
2. Will this universe expand indefinitely?
In both cases, interesting theoretical issues
are at stake, not just practical action:
 We make such predictions to help us
deepen our theoretical understanding.
 It is scientifically legitimate to forecast.
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Induction here to stay
In sum:
Salmon argues that we need induction for
practical decision making.
We will also need it in science, even
theoretical science.
Logically, we could eliminate induction from
reasoning, but that would leave us with a
theoretical and practical repertoire that is
severely impoverished.
15
Justifying induction pragmatically
Reichenbach offers a strategy similar to that
of Popper/Watkins in that it is a pragmatic
justification.
However, he offers a little bit more by way
of justifying the rationality of induction.
Let us examine his views…
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Reichenbach’s take on the problem
Reichenbach: Hume is right:
 We can’t prove that the conclusion of an
inductive inference must be true.
But the real question is: is induction useful
when trying to decide how to act?
It does seem possible to justify induction
according to this standard. For example,
perhaps we can show that:
Induction is the best guide to action that we
have (even if not that good).
If this is the case, then the principle is
justified.
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An analogy
Suppose S is dying.
 The doctor says: There are no known
drugs or therapies that will save S.
 However, it is possible that this
operation will remove the disease, but I
don’t know that with any certainty.
Reichenbach: It is justified to perform the
operation.
 It is the best (and only) hope.
Similarly: if induction turns out to be the best
way to guide our lives, then it is justified to
follow it even if we can’t prove it will work.
 Okay, but can we show that induction is
the best principle here?
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Reichenbach: Two possibilities:
1. The world is ordered.
2. The world isn’t ordered.
If #2, then no method of prediction will work.
 So, using induction is no better but also
no worse than anything else.
So, using induction is as justified as
anything can be.
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Induction in an orderly world
Assume, now, that the world is ordered.
Then: any method of determining patterns
of event occurrence will have to:
 Examine past frequencies.
 Project them into the future.
In other words, all methods of empirical
science depend on induction.
 So if any works, induction will work.
 If induction doesn’t work, nothing else
will.
Either way, induction is justified as the best
(only) approach we have.
So: whether the world is ordered or not, the
best approach you can take to guiding your
actions is the inductive approach. It is,
therefore, justified.
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Comparison with decision theory
World is
Ordered
Good
Reason
inductively predictions
Don’t reason Bad (no)
inductively Predictions
World Isn’t
ordered
Bad (no)
predictions
Bad (no)
Predictions
One action, A, dominates another action, B,
iff, in all possible situations, the
consequences of selecting A over B are at
least as desirable as those of selecting B
over A and sometimes better
“Sure-thing (or dominance) principle”: the
action is best which dominates the others.
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Problem
This doesn’t show very much.
 Even if induction is necessarily the best
principle we have, it doesn’t follow that it
is a very good one.
Reichenbach: that’s just our predicament!
 The best we can do is to make our bets
to the best of our abilities.
 There’s nothing we can do about the
fact that future is at best uncertain.
22
Comparison with Popper
Note that Popper also insists that we base
predictions on theories that have been
successful in the past because it is all we
have to go on.
 But he simply assumes that this renders
the view rational, i.e. everything else we
might go on is comparatively irrational.
Reichenbach’s position is different. He
aims to show that induction, even if
irrational, is the most rational prediction we
could possibly have.
 He doesn’t assume this.
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At least a little rationality
Recall that Reichenbach argues that
rational prediction can only succeed in a
patterned world, and that in such a world
induction is the best guide available.
Nothing else could match it: not tossing a
coin, not counting vowels, etc.
 Only a careful examination of past
sequences and the formulation of
general rules on that basis could
possibly give a better than chance
probability of correct predictions.
 So, induction is the only chance we
have to go above 50-50 guesses.
In this way Reichenbach presents us with a
pragmatic defence of induction that differs
from Popper’s.
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Some problems remain
Reichenbach has, perhaps, given us reason
to use induction.
But he has not given us any reason to
believe conclusions based on inductive
reasoning are likely to be true or that such
reasoning is in fact rational.
This still seems unsatisfactory.
Is it plausible to suppose that, say, all your
years of experience preferring elevators
over window-leaps gives you no reason to
believe elevator will continue to be safer?
Is it reasonable to suppose that all you
could believe is: we have no idea whether
elevators will be safer tomorrow, but
practically that is the best thing to believe?
Do you really not believe they will be safer
tomorrow?
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Any hope left?
It would be nice if we could come up with an
inductive logic or program that would entitle
one to have confidence in the actual beliefs
formed as the result of inductive reasoning.
So far, nobody has shown us a way to do
this.
But let us keep searching.
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