A syllogism is an act of reasoning; i.e. deducing one truth from another. Logicians speak of three operations of the mind; apprehension, judgment, and reasoning.
- Apprehension is just a single word or object in the mind such as “dog”.
- A judgment or a proposition is taking two such apprehensions or words and affirming or denying something of each; e.g. “Dogs are friendly” or “Dogs have a marvelous sense of smell.”
- When our minds reason, they take two judgments and deduce a third from the truth (or falsity) of the others. A syllogism is simply laying out these judgments in a linear way.
For example,
- All dogs are friendly;
- Rex is a dog;
- Therefore, Rex is friendly.
These different propositions are called “premises”.
| All dogs are friendly; | Major Premise |
| Rex is a dog; | Minor Premise |
| Therefore, Rex is friendly. | Conclusion |
The conclusion of a syllogism is a necessary truth; i.e. it must be true.
There are three kinds of syllogisms:
- categorical,
- hypothetical, and
- disjunctive.