Premise
In all observed instances X has property Y.
Conclusion
In all instances X has property Y.
Figure 6.1 Illustration of Induction
Bird life provides two contrasting examples where this reasoning provides a
correct answer in one instance but not in the other. First, the crow:
Premise
In all observed instances crows are black
Conclusion
All crows are black.
Figure 6.2 Illustration of Induction
Now for swans. Here is an induction for them:
Premise
In all observed instances swans are white.
Conclusion
All swans are white.
Figure 6.3 Illustration of Induction
In the case of the crow the conclusion is correct. In the case of the swan, the
conclusion is true for European swans. Australia, however, has the black swan
so the conclusion is not universally true.
The weak form of induction is based on excessively limited observation,
which can easily happen when observing oneself. “I always have a cup of tea
first thing in the morning so obviously everyone else does do”. Here, the good
sense of starting the day with a cup of tea does not carry over into good
reasoning.
David Hume (1711-1776) made the pertinent comment that most of us live our
lives based on induction. Food has always nourished us in the past so
we
assume that it will do so in the futre. As Hume pointedly commented,
someone who insisted on sound deductive justifications for everything would
starve to death.
To emphasise the point, in contrast to deduction which reasons from the
general to the particular, induction reasons from the particular to the general.
Induction, therefore, does not constitute a watertight an argument in the way
that deduction function, so it does not satisfy requirements of abstract
intellectual stringency. Its conclusions
are merely possible, and at best
probable. Nevertheless, induction is a useful means of reasoning in the real
world. Indeed, this very weakness of induction confers an advantage which is
lacking with deduction in that it discovers new relationships. In fact, many
laws of science are based on induction. Deduction, by contrast, will only
reveal relationships that are already known or knowable.
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