induction (logic and rhetoric)

English logician Isaac Watts (1674-1748) on the power of induction.

Induction is a method of reasoning that moves from specific instances to a general conclusion. Also called inductive reasoning.

In an inductive argument, a rhetor (that is, a speaker or writer) collects a number of instances and forms a generalization that is meant to apply to all instances. (Contrast with deduction.)

In rhetoric, the equivalent of induction is the accumulation of examples.

Examples and Observations

  • "Induction operates in two ways. It either advances a conjecture by what are called confirming instances, or it falsifies a conjecture by contrary or disconfirming evidence. A common example is the hypothesis that all crows are black. Each time a new crow is observed and found to be black the conjecture is increasingly confirmed. But if a crow is found to be not black the conjecture is falsified."
    (Martin Gardner, Skeptical Inquirer, Jan.-Feb., 2002
  • "If you have trouble remembering the difference between inductive and deductive logic, consider their roots. Induction comes from Latin for 'to induce' or 'to lead.' Inductive logic follows a trail, picking up clues that lead to the end of an argument. Deduction (both in rhetoric and expense accounts) means 'to take away.' Deduction uses a commonplace to pull you away from your current opinion."
    (Jay Heinrichs, Thank You for Arguing: What Aristotle, Lincoln, and Homer Simpson Can Teach Us About the Art of Persuasion. Three Rivers Press, 2007
  • "Inductively valid, or correct, arguments, unlike deductively valid ones, have conclusions that go beyond what is contained in their premises. The idea behind valid induction is that of learning from experience. We often observe patterns, resemblances, and other kinds of regularities in our experiences, some quite simple (sugar sweetening coffee), some very complicated (objects moving according to Newton's laws--well, Newton noticed this, anyway). . . .

    "Here is a simple example of an inductively valid argument of the kind sometimes called induction by enumeration:
    I loaned my friend $50 last November and he failed to pay me back. (Premise) I loaned him another $50 just before Christmas, which he hasn't paid back (Premise), and yet another $25 in January, which is still unpaid. (Premise) I suppose it's time to face facts: He's never going to pay me back. (Conclusion)
    "We use inductive reasoning so frequently in everyday life that its nature generally goes unnoticed."
    (H. Kahane and N. Cavender, Logic and Contemporary Rhetoric, 1998)

    F.D.R.'s Use of Induction

    • "The following passage comes from Franklin D. Roosevelt's speech to Congress on December 8, 1941, the day after Pearl Harbor, declaring a state of war between the United States and Japan.
      Yesterday the Japanese government also launched an attack against Malaya.

      Last night, Japanese forces attacked Hong Kong.

      Last night, Japanese forces attacked Guam.

      Last night, Japanese forces attacked the Philippine Islands.

      Last night, the Japanese attacked Wake Island.

      And this morning, the Japanese attacked Midway Island.

      Japan has, therefore, undertaken a surprise offensive extending throughout the Pacific area. (Safire 1997, 142; see also Stelzner 1993)
      Here Roosevelt has in effect constructed a comparison that involves six items, and his purpose in doing so appears in the final sentence. His 'therefore' signals that he offers a conclusion supported by the preceding list, and these individual instances have been united as examples for the conclusion on the basis of their parallel form. . . . The argument form here, supporting a generalization with examples, is classically known as induction. In the most direct manner, the six examples of Japanese aggression 'add up' to the conclusion. The list strengthens what was already, on the occasion of Roosevelt's speech, an overwhelming case for war."
      (Jeanne Fahnestock, Rhetorical Style: The Uses of Language in Persuasion. Oxford Univ. Press, 2011)

      The Limits of Rhetorical Induction

      • "It is important to remember that rhetorical induction does not actually prove anything; it is arguing from the probability that known instances are parallel to and illuminating of those less well known. Whereas full logical induction enumerates all possible instances, the rhetorical argument by example almost always enumerates less than the total. The persuasive impact of such a method of reasoning is increased, of course, as one increases the number of examples."(Donald E. Bushman, "Example." Encyclopedia of Rhetoric and Composition: Communication From Ancient Times to the Information Age, ed. by Theresa Enos. Taylor & Francis, 1996)

      Pronunciation: in-DUK-shun

      From the Latin, "to lead in"