Deduction; Induction; and Abduction

A little taste of something I prepared for my students studying the MBA…

We tend to think there are two types of reasoning:

  • deduction, where we move with logical certainty from general principles to a particular conclusion, as in “all swans are white, this is a swan, so this must be white”
  • and induction, where we move from particular observations to general principles, as in “all the swans that have ever been seen are white, so all swans are white”

Deduction is infallible as long as the premises are true, while induction yields probabilities that can always be falsified by events – the black swans that turn up when no one is expecting them.

Black Swan…

There is another, more conjectural kind – sometimes called abductive reasoning – that can’t offer certainty or any precise assessment of probability, only the best available account of events. Importantly, this kind of reasoning can’t be practised simply by following rules.

Sherlock Holmes and Watson

“When you have excluded the impossible, whatever remains, however improbable, must be the truth.”

See also:


3 thoughts on “Deduction; Induction; and Abduction

  1. Pingback: Logical Reasoning | Logic, Reasoning, Argumentation

  2. garcanad

    I suppose it can come to a point when one would question the definition of ‘truth’.
    It reminds me of a quotation from Tao Te Ching, used by a famous Software Engineering professor as an intro to a lecture on formal specification:
    (very loosely/crudely translated here as ‘Any ‘law/truth’ etc. that can be stated will not be permanent’)
    It proved to be absolutely TRUE in formal software specification. (‘abductive reasoning’ here?)


    1. ukgardenfiend Post author

      Truth is in the eye of the beholder? And is variable? I said something about this before when I commented about my philosophy which is based – loosely – on Sartre – the world is what I want it to be and you are here because I see you as being here… I’m interested though that your software Engineering prof should think that way, as mine was the complete opp which was why I struggled with it!



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