What Is Deductive Reasoning?

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Deduction is a method of reasoning from the general to the specific. Also called deductive reasoning and top-down logic.

In a deductive argument, a conclusion follows necessarily from the stated premises. (Contrast with induction.)

In logic, a deductive argument is called a syllogism. In rhetoric, the equivalent of the syllogism is the enthymeme.​

See Examples and Observations below. Also, see:

Etymology

From Latin, "leading"

Examples and Observations

  • "The fundamental property of a deductively valid argument is this: If all of its premises are true, then its conclusion must be true also because the claim asserted by its conclusion already has been stated in its premises, although usually only implicitly.
  • Scientific Deduction and Rhetorical Deduction
    "For Aristotle, scientific deduction differs in kind from its rhetorical counterpart. True, both are conducted according to the 'laws' of thought. But rhetorical deduction is inferior for two reasons: it starts with uncertain premises, and it is enthymematic: it generally relies on audience presuppositions to supply missing premises and conclusions. Because conclusions cannot be more certain than their premises and because any argument is deficient in rigor that relies on audience participation for its completion, rhetorical deductions can yield at best only plausible conclusions. . . .
  • Syllogisms and Enthymemes
    "Very rarely in literary argument do reasoners make use of the complete syllogism, except to render perfectly apparent the premises from which the conclusion is deduced, or to show some fault in reasoning. Deductive arguments take various forms. One premise, or even the conclusion, may not be expressed if obvious enough to be taken for granted; in this case, the syllogism is called an enthymeme. One of the premises may be conditional, which gives the hypothetical syllogism. A syllogistic argument may be involved in a statement with its reasons, or with its inferences, or may be diffused throughout an extended discussion. To argue effectively, with clearness and cogency, the reasoner must have his deductive framework clearly in mind at every point of his discussion, and keep it before the reader or hearer."

    Pronunciation

    di-DUK-shun

    Also Known As

    Deductive Argument

    Sources

    H. Kahane, Logic and Contemporary Rhetoric, 1998

    Alan G. Gross, Starring the Text: The Place of Rhetoric in Science Studies. Southern Illinois University Press, 2006

    Elias J. MacEwan, The Essentials of Argumentation. D.C. Heath, 1898

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    Your Citation
    Nordquist, Richard. "What Is Deductive Reasoning?" ThoughtCo, Apr. 4, 2017, thoughtco.com/deduction-logic-and-rhetoric-1690422. Nordquist, Richard. (2017, April 4). What Is Deductive Reasoning? Retrieved from https://www.thoughtco.com/deduction-logic-and-rhetoric-1690422 Nordquist, Richard. "What Is Deductive Reasoning?" ThoughtCo. https://www.thoughtco.com/deduction-logic-and-rhetoric-1690422 (accessed September 24, 2017).