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The Big Questions: Philosophy of Science Handout 1
Dr. H. Beebee
The Problem of Induction
Is science a rational enterprise?
One of the aims of science, perhaps its most fundamental aim, is knowledge of laws of
nature. So if we want to know if the scientific enterprise can be rational, we need to see
if there is some method by which one can attain knowledge of laws of nature. (Then we
can see if science
is
rational by asking whether it uses that method.)
Laws of nature
For now, think of a law of nature as being a general truth, e.g:
All gases at the same temperature & pressure contain the same number of
molecules per unit volume
All metals expand when heated.
All bodies fall with constant acceleration.
These all have the general form ‘All Fs are Gs’: they are
universal generalisations
(UGs
for short).
This contrasts with singular statements like ‘this piece of copper expanded when
heated’ or ‘that stone fell with constant acceleration’.
The big question:
Given that one only has singular statements to go on, how can
one come to know the truth of a UG?
A popular answer:
By “inductive inference”, which takes the general form:
(*)
This F is G
That F is G
:
:
Therefore
ll Fs are Gs
In other words, we may
infer
, by inductive inference, that a general law (“all Fs are
Gs”) holds when we have observed a sufficient number of
instances
of the law (“this F
is G”, etc.).
BUT . . . .
David Hume, an 18th century Scottish philosopher, argued famously that we can have
no knowledge of general laws. His argument can be reconstructed as follows:
Hume’s argument
(1)
Beliefs about general laws are attained by inductive inference
(2)
Inductive inference is unjustified
(3)
If a belief is unjustified, it does not count as knowledge.
Therefore
We cannot have knowledge of general laws.
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Each of Hume’s premises seems intuitively plausible. But the conclusion is one which
most scientists and philosophers do not like. If we can never know any general law,
what’s the point of doing science?
Saving scientific knowledge: some responses to Hume's Argument
One kind of response to Hume’s argument is to try and find a way of undermining
premise 2, by showing that inductive inferences can be justified after all.
Solution 1: A naive approach
Make sure your observed instances come from a wide enough variety of different
conditions. (The inference to ‘All swans are white’ was bad inductive practice: nobody
looked in Australia.)
First response : There’s no
a priori
way of telling what counts as ‘wide enough’ or what
counts as ‘different conditions’. Do you need to make an observation in every country
or just every continent? Do you need to vary the time of day or the clothes you wear
when you run the experiment?
Second response : It’s not just a matter of varying the conditions. Suppose you knew
that all metals have expanded when heated up until now. ‘All metals expand when
heated’ says more than this: it says they’ll continue to do so in the future. But how can
you know that they will? (You can’t go to the future to find out!)
Solution 2: Principle of Uniformity of Nature
To get around the second response, assert a principle of uniformity of nature, or as
Popper puts it, of ‘the immutability of natural processes’: in effect, assert that the future
will be like the past.
Response : What grounds are there for asserting such a principle? By inference from
past success:
But this argument has essentially the same form as (*): it employs the very inference
we’re currently trying to justify. Solution 2 is circular.
Solution 3: Inductive justification of induction
Inductive inference was successful on occasion
x
Inductive inference was successful on occasion
y
Inductive inference is always successful
Response : Again, inductive inference is being used to justify inductive inference. In
any case, the conclusion is manifestly false: remember ‘All swans are white’.
2
On all previous occasions the future has resembled the past
Therefore, the future will always resemble the past
Solution 4: ‘The retreat to probability’
OK, inductive inferences don’t
always
work, but they’re
very likely
to lead to true
conclusions.
Response 1 : The new form of inference isn’t really different to (*) - it still goes from
the particular to the general. So the retreat doesn’t help.
This F is G
That F is G
Therefore
Probably, all Fs are Gs
Response 2 : UGs cover an infinite number of possible cases. So even if the above
argument form were valid, reasoning from a finite number of observed cases would
confer zero probability on the conclusion.
Solution 5: Induction is rational by definition
Anyone who understands the meaning of the term ‘rational’ will tell you that predicting
future regularities on the basis of past observation is rational. So it is.
Response : This just avoids the original problem: sure, most people
think
induction’s
rational, but that’s because they mistakenly think that there’s some way of justifying it.
Suggested reading
Call numbers beginning with B are to be found in the Chifley Library; Q call numbers
are in the Hancock Library.
D. Hume
Treatise of Human Nature
(B1485 1951/1978), Book I, Part III,
or:
Enquiry concerning Human Understanding
(B1455.S4), section IV
P. Edwards & A. Pap (eds.):
A Modern Introduction to Philosophy
(BD21.E4),
section on induction
A. Chalmers
What Is This Thing Called Science?
(Q175.C446), chapters 1 & 2
J.S. Mill
System of
Logic (B1603.S9), Book III, chs. I-IV and XXI (especially
III & XXI) (reprinted in Edwards & Pap)
B. Russell
Problems of Philosophy
(BD21.R8), chapter 6 (reprinted in Edwards &
Pap)
A. O’Hear
An Introduction to the Philosophy of Science
(Q175.O454), chs. 1 & 2
Also Bird's Book extract #2 (induction) on the readings page of the course website.
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