Mohammed asked:

I know that deductionis a kind of inference in which the truth of premises determine/prove the truth
of the conclusion, inductionis a kind of inference in which the truth of premises just supports the
truth of the conclusion.

But I've read some other texts which have confused me, expressing that the direction of inquiry from
knowledge of a universal to knowledge of its particulars is 'deduction', and that from knowledge of
particulars to knowledge of their universal is 'induction'. If the latter definitions are wrong then tell me
what labels/terms should be given to those types of inquiry.

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Here are some key characteristics of deductive and inductive arguments that should help clear up
your confusion:

Deductive:

*There is no possible situation where all the premises are true and the conclusion false. In other
words if the premises are true the conclusion mustbe true.

*All the information in the conclusion is already contained in the premises.

*The inference moves from a universal to a particular claim.

Inductive:

*If the premises are true, the conclusion is probablytrue.

*the information in the conclusion exceeds that given in the premises.

*The inference moves from a particular claim to a universal or law-like conclusion.

So the reason why the inference in deductive arguments involving universal propositions is from
universal to particulars rather than the other way round is because we have all the information about
what the conclusion will contain already in the premises. Let me give an example:

Premise 1: All monkeys drink Guinness. Premise 2: Harry is a monkey.
Conclusion: Harry drinks Guinness.

Premise 1 is a law like, universal statement. (It does not matter that Premise 1 is actually false, since
we are concerned with any possible situation. It could be that in an alternative universe monkeys do
drink Guinness.) Premise 2 tells us about a monkey, i.e. Harry, so we already know, at least implicitly,
that Harry drinks Guinness. The inference to the conclusion makes that knowledge explicit.

Moving on, induction has caused heaps of people heaps of trouble, so we will keep it simple. In
inductive arguments we start with some claim (usually based on experience) and infer some general
conclusion. For example:

Premise: Every time I have been fishing in the past I have caught a big fish. Conclusion: Every
time I go fishing I will always catch a big fish.

The conclusion is a general claim but clearly it is at best only probable since the day may come when
I do not catch a big fish. So in induction the premise does not provide any guarantee of the truth of
the conclusion, since the conclusion is meant to go beyond the information we have in the premise.

Brian Tee
Dept of Philosophy
University of Sheffield.