Logic

Can someone please explain to me the difference between induction and deduction? I think I get it, but merely reading it in books is not enough!!! Thanks!

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In deduction, the move from premises to conclusions is such that if the premises are true, then the conclusion must also be true. For example, take the following argument:

1. Elvis Presley lives in a secret location in Idaho.

2. All people who live in secret locations in Idaho are miserable.

3. Therefore Elvis Presley is miserable.

If the two premises are true, then it must be true that Elvis is miserable. Note, however, that if Elvis doesn’t exist any longer, then the conclusion need not be true either. But IF 1 and 2 are true, then so is 3.

Unlike deductive inferences, induction involves an inference where the conclusion follows from the premises not with certainty but only with probability.

Often, induction involves reasoning from a limited number of observations to wider, probable generalisations. Reasoning this way is commonly called "inductive generalization." It’s a kind of inference that usually involves reasoning from past regularities to future regularities. One classic example is the sunrise. The sun has risen regularly so far as human experience can recall, so people reason that it will probably rise tomorrow. (The work of 18th-century Scottish philosopher David Hume has been influential on this score.) This sort of inference is often taken to typify induction.

But induction is not essentially defined as reasoning from the specific to the general. An inductive inference need not be past-future directed. And it can involve reasoning from the general to the specific, the specific to the specific or the general to the general. Indeed, there are even deductive inferences that move from the specific to the general.

One could, for example, reason inductively from the more general, past-oriented claim that no trained athlete on record has been able to run one hundred metres in less than nine seconds, to the more specific past-oriented conclusion that my friend had probably not achieved this feat when he was at university, as he claims.

Reasoning through analogies (see Analogies) as well as typical examples and rules of thumb are also species of induction, even though none of them involves moving from the particular to the general.

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