8

What is the difference between deduction and inference?

My guess is that deduction is a more concrete and restricted opinion because it involves logic every time whereas inference is a mere guess on the given evidences or situations and it involves logic sometime.

What does Sherlock Holmes do? Is it deduction or inference?

  • Since programming languages always refer to (type) inference (e.g. C#, Swift) when they assign a type to a variable based upon the value assigned to it, I can almost certainly say that inference is not a mere guess but an accurate, 100% precise affirmation based upon the given clues. – ccalboni Aug 2 '14 at 23:05
9

To deduce and infer are largely interchangeable, but...

deduce is more likely to be used where you arrive at some conclusion after a more prolonged logical analysis of relevant factors (which may not even be readily apparent until actively sought out).

Whereas you often infer a conclusion almost instantly, from directly-observable factors.

Since Sherlock is the archetypal solver of complex/non-obvious mysteries, he tends to deduce...

Holmes deduced [something] (about 709 results in Google Books)
Sherlock deduced it. (186 results)
Holmes inferred it (100 results)
Sherlock inferred it (5 results)

I personally don't recognise OP's formal logical reasoning vs inspired guess distinction, except insofar as it may reflect the above tendency for deduction to sometimes be a more lengthy process.

3

"Deduction," is the logical process of prediction based on a large number of samples or experience.

"Inference," is the logical process of prediction based on anecdotal, or a relatively small sample.

They are not at all interchangeable.

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