The Logic of Inquiry: Induction

Inductive arguments do not demonstrate the truth of their conclusions, but merely establish probability. Yet most scientific proof is based on inductive arguments, hence the question of whether science deals with “truth” or merely “predictive usefulness.”

Inductive Arguments

Basically, induction is argument from analogy. The best discussion of induction is still J.S. Mills’ “Canons of Induction.” Mills set out five rules for induction:

Agreement: Similar outcomes share similar circumstances
Difference: Dissimilar outcomes in otherwise similar circumstances
Joint Method: Both agreement & differences are observed
Residues: Subtracting known outcomes and their circumstances, remaining circumstances must explain outcomes
Concomitant Variation: If circumstances and outcomes vary together, they are cause and effect, or else are connected through some other cause and effect.

You will notice that induction is much less cut-and-dried than the syllogism. That is what makes science so interesting—there is always the possibility that the residual approach will pull something out of what seems to be nothing, or that concomitant variation will disclose that what seemed to be causation was really only co-relation.

Over time, additional rules of thumb have developed for arguing increased confidence for inductive conclusions:

Number of cases from which the induction was drawn
Number of respects in which cases are similar
Strength of conclusion, relative to the strength of its premises
Number of respects in which cases from which the induction was drawn are dissimilar
Strength of dissimilarity in the way the premises are developed
Strength of the similarities among the results

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