Pronunciation: sil-uh-JIZ-um

In logic, a form of deductive reasoning consisting of a majorpremise, a minor premise, and a conclusion. Adjective: syllogistic.

Here is an example of a valid categorical syllogism:

Major premise: All mammals are warm-blooded.
Minor premise: All black dogs are mammals.
Conclusion: Therefore, all black dogs are warm-blooded.

 

In rhetoric, an enthymeme is an informally stated syllogism.

See also:

• Toulmin Model
• Validity

 

Etymology:

From the Greek, "to infer, count, reckon"

Examples and Observations:

• "The process of deduction has traditionally been illustrated with a syllogism, a three-part set of statements or propositions that includes a major premise, a minor premise, and a conclusion.

  Major premise: All books from that store are new.
  
  Minor premise: These books are from that store.
  
  Conclusion: Therefore, these books are new.

• The major premise of a syllogism makes a general statement that the writer believes to be true. The minor premise presents a specific example of the belief that is stated in the major premise. If the reasoning is sound, the conclusion should follow from the two premises. . . .
  
  "A syllogism is valid (or logical) when its conclusion follows from its premises. A syllogism istrue when it makes accurate claims--that is, when the information it contains is consistent with the facts. To be sound, a syllogism must be both valid and true. However, a syllogism may be valid without being true or true without being valid."
  (Laurie J. Kirszner and Stephen R. Mandell, The Concise Wadsworth Handbook, 2nd ed. Wadsworth, 2008)



• "In building his theory of rhetoric around thesyllogism despite the problems involved in deductive inference Aristotle stresses the fact that rhetorical discourse is discourse directed toward knowing, toward truth not trickery. . . . If rhetoric is so clearly related to dialectic, a discipline whereby we are enabled to examine inferentially generally accepted opinions on any problem whatsoever (Topics 100a 18-20), then it is the rhetoricalsyllogism [i.e., the enthymeme] which moves the rhetorical process into the domain of reasoned activity, or the kind of rhetoric Plato accepted later in the Phaedrus."
  (William M.A. Grimaldi, "Studies in the Philosophy of Aristotle's Rhetoric." Landmark Essays on Aristotelian Rhetoric, ed. by Richard Leo Enos and Lois Peters Agnew. Lawrence Erlbaum, 1998)



• "LOGIC, n. The art of thinking and reasoning in strict accordance with the limitations and incapacities of the human misunderstanding. The basic of logic is the syllogism, consisting of a major and a minor premise and a conclusion--thus:
  Major Premise: Sixty men can do a piece of work sixty times as quickly as one man.
  Minor Premise: One man can dig a posthole in sixty seconds;
  therefore--
  Conclusion: Sixty men can dig a posthole in one second. This may be called the syllogism arithmetical, in which, by combining logic and mathematics, we obtain a double certainty and are twice blessed."
  (Ambrose Bierce, The Devil's Dictionary)



• "On Meet the Press, . . . [Tim] Russert reminded [George W.] Bush, 'The Boston Globe and the Associated Press have gone through some of their records and said there's no evidencethat you reported to duty in Alabama during the summer and fall of 1972.' Bush replied, 'Yeah, they're just wrong. There may be no evidence, but I did report. Otherwise, I wouldn't have been honorably discharged.' That's the Bush syllogism: The evidence says one thing; the conclusion says another; therefore, the evidence is false."
  (William Saletan, Slate, Feb. 2004)



• Dr. House: Words have set meanings for a reason. If you see an animal like Bill and you try to play fetch, Bill's going to eat you, because Bill's a bear.
  Little Girl: Bill has fur, four legs, and a collar. He's a dog.
  Dr. House: You see, that's what's called a faulty syllogism; just because you call Bill a dog doesn't mean that he is . . . a dog.
  ("Merry Little Christmas, House, M.D.)