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Definition:

A method of reasoning from the general to the specific.

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 also:

Etymology:

From Latin, "leading"

Examples and Observations:

  • Sherlock Holmes and Watson were on a camping trip. They had gone to bed and were lying there looking up at the sky. Holmes said, "Watson, look up. What do you see?"
    "I see thousands of stars."
    "And what does that mean to you?"
    "I guess it means we will have another nice day tomorrow. What does it mean to you, Holmes?"
    "To me, it means someone has stolen our tent."


  • "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.

    "Here is an example of a very simple deductively valid argument:

    Everything made of copper conducts electricity. (Premise)
    This wire is made of copper. (Premise)
    This wire will conduct electricity. (Conclusion)

    Taken alone, neither premise makes the claim that the wire will conduct electricity; but taken together, they do, although not explicitly."
    (H. Kahane, Logic and Contemporary Rhetoric, 1998)


  • "You'd like to think that, wouldn't you? You've beaten my giant, which means you're exceptionally strong, so you could've put the poison in your own goblet, trusting on your strength to save you, so I can clearly not choose the wine in front of you. But, you've also bested my Spaniard, which means you must have studied, and in studying you must have learned that man is mortal, so you would have put the poison as far from yourself as possible, so I can clearly not choose the wine in front of me."
    (Vizzini in The Princess Bride, 1987)


  • Syllogisms and Ethymemes
    "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."
    (Elias J. MacEwan, The Essentials of Argumentation. D.C. Heath, 1898)
Pronunciation: di-DUK-shun
Also Known As: deductive argument
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