A term you'll meet in logic and rhetoric.
A syllogism is a three-part deductive argument, formalised by Aristotle in the Prior Analytics (c. 350 BCE), consisting of a major premise, a minor premise, and a conclusion that follows necessarily from the two premises. The standard textbook example:
All men are mortal. (major premise)
Socrates is a man. (minor premise)
Therefore, Socrates is mortal. (conclusion)
The syllogism is the basic unit of formal Western logic and the engine of most rhetorical argument for two and a half thousand years. To understand much of philosophical and legal writing, you need to be able to identify the form.
A syllogism has three terms (e.g., men, Socrates, mortal) distributed across the two premises and the conclusion. Each premise contains two of the three; the conclusion contains two; the term that appears in both premises but not the conclusion is the middle term. The middle term is what makes the inference possible.
Aristotle catalogued the valid forms of syllogism by which of the four basic premise-types they used:
The combinations that produce valid syllogisms are a small subset of the possible combinations. Medieval logicians gave the valid forms mnemonic names — Barbara, Celarent, Darii, Ferio — that survive in introductory logic courses.
A crucial distinction:
A valid syllogism can have false premises. "All cats are fish. Garfield is a cat. Therefore, Garfield is a fish." The form is valid; the major premise is false; the conclusion is correspondingly false. Distinguishing form-correctness from content-correctness is the elementary move of formal logic.
In actual speech and writing, syllogisms rarely appear fully spelled out. The everyday version is the enthymeme — a syllogism with one premise suppressed, left for the audience to supply.
"You should listen to her — she's a doctor" is an enthymeme. The suppressed major premise is something like "Doctors are credible authorities on medical matters." The audience fills it in.
Most political speech runs on enthymemes. The art of the enthymeme is choosing which premise to suppress — usually the one the audience already agrees with, so the argument feels like common sense rather than persuasion.
Several literary uses:
Syllogistic reasoning underlies almost all formal Western argument. Legal briefs, scientific reasoning, ethical philosophy, theological dispute — all use syllogistic forms. Recognising syllogisms in argumentative writing lets you identify both what is being argued and which premise is doing the work.
The "suppressed premise" is often the most important political move. When a writer announces a conclusion that seems to follow from evidence, ask which major premise has been quietly assumed. The argument's strength usually depends on whether the audience accepts the unstated premise — and the writer chose not to state it precisely because it might not survive being said aloud.
When reading argumentative prose — an essay, a sermon, a political speech, a legal opinion — try restating the argument as an explicit syllogism. The exercise often reveals the suppressed premise. If the suppressed premise is true and relevant, the argument is sound. If it is false, doubtful, or question-begging, the argument is rhetorical theatre dressed up as logic.
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