Syllogism is the classic form of argument: two premises that, together, guarantee a conclusion. It is the oldest and most studied structure of Western logic, and it still organizes any good reasoning today.
The two thousand year old example
All men are mortal; Socrates is a man; therefore, Socrates is mortal. This syllogism has been cited for centuries because it exposes, in the simplest way possible, the mechanics of any valid deduction: the first premise is general, the second fits a particular case within it, and the conclusion is what necessarily remains, if the two premises are true.
Why form matters as much as content
The syllogism separates two questions that are often mixed up: is the structure correct? And are the premises true? A syllogism can have impeccable form and still produce a false conclusion, when the premise is false: all fish fly; salmon is fish; therefore, the salmon flies. The syllogism structure is correct, but the first premise is not true, and so the conclusion collapses.
It was Aristotle who systematized this form in his treatises on logic, creating the basis on which all subsequent formal logic was built. The intuition behind it is simple: if I accept that every A is B, and that this C is A, I am obliged, by the structure of reasoning itself, to accept that this C is B.
Where does the syllogism appear today
Nobody talks about "syllogism" in a social media discussion, but the structure is always there, embedded. Every argument that sounds logical is, at bottom, an attempt at a syllogism, sometimes successful, sometimes hiding a false premise or a "therefore" that does not hold up. Learning to recognize the syllogism behind someone else's speech is the first step in separating the reasoning that is gold from that which only glitters, a topic covered in more depth in premises, conclusion and validity.
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What is a syllogism?
It is a form of argument composed of two premises and a conclusion, in which the conclusion necessarily follows from the premises. The classic example: all men are mortal; Socrates is a man; Therefore, Socrates is mortal.
Who first described the syllogism?
Aristotle, in his treatises on logic collected under the name Organon, systematized the form of the syllogism as the basis of valid deductive reasoning.
Does a syllogism always reach a true conclusion?
Not necessarily. The structure can be valid even with false premises, which produces a conclusion without real guarantee, as in "all fish fly; salmon are fish; therefore, salmon fly".
Continue in the cluster of this class: Premises, conclusion and validity · What is a premise · Difference between truth and validity
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