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.

  1. Apprehension is just a single word or object in the mind such as “dog”.
  2. 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.”
  3. 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:

  1. categorical,
  2. hypothetical, and
  3. disjunctive.

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