What Is Syllogism?

A syllogism is a rhetorical device that begins with a major statement, known as a premise, narrows down to a minor statement, or premise, and then arrives at a conclusion using deductive reasoning. The simplest way to explain how this works is by giving examples:

  • Major premise: All men are mortal. Minor premise: Socrates is a man. Conclusion: Socrates is mortal. (This is an example of Aristotle’s famous “Barbara” syllogism.)
  • Major premise: Plants need to carbon dioxide to live. Minor premise: The oak tree is a plant. Conclusion: The oak tree needs carbon dioxide to live.

A compressed syllogism, called an enthymeme, combines the minor premise and conclusion; the major premise is implied. For instance, “Socrates is mortal because he is a man.”

It’s easy to commit a logical fallacy using syllogisms. Take a look at this example:

  • Major premise: All women like to shop. Minor premise: John likes to shop. Conclusion: John is a woman.

Leaving aside the questionable major premise, that all women like shopping, you cannot make a deduction based on this false logic. In order for a syllogism to work, the minor premise must be a valid category within the major premise, and both premises must be true. There are 256 types of categorical syllogism alone!

Another type of syllogism that is ripe for syllogistic fallacy is the conditional syllogism:

  • Major premise: If Lucinda smokes cigarettes every day, she increases her risk of lung cancer. Minor premise: Lucinda doesn’t smoke cigarettes every day. Conclusion: Lucinda has no increased risk of lung cancer.

This syllogism appears logical, but what if Lucinda’s husband is a chain smoker?

Syllogistic fallacy isn’t just a failure of logic. It is also a kind of wit that people have relied on for centuries to forward ridiculous conclusions while pretending to use reason.

Examples of Syllogism and Syllogistic Fallacy

Syllogism Example 1. “Flavius: Have you forgot me, sir? /Timon: Why dost ask that? I have forgot all men; Then, if thou grant’st thou’rt a man, I have forgot thee.” This witty syllogism occurs in Shakespeare’s historical play, Timon of  Athens.

Syllogism Example 2. All birds lay eggs. A chicken lays eggs. A chicken is a bird.

Syllogism Example 3. All dogs bark. The basenji, which is mute, cannot bark. A basenji is not a dog.

Syllogism Example 4. All swans are white. A cygnet (baby swan) is gray. A cygnet is not a swan.

Syllogism Example 5. All books contains words. A shopping list contains words. A shopping list is a book.

(View all literary devices)