10 Rules for a valid categorical syllogism

The 10 rules for a valid categorical syllogism are the following:

Rule 1. There should only be three terms in a categorical syllogism. They are the Major Term, the Minor Term, and the Middle Term.

Rule 2. A categorical syllogism is composed of only three categorical propositions. Each term must occur in two propositions in the syllogism.

Rule 3. The terms in the conclusion may only be universal if they are universal in the premises.

Rule 4. The middle term must occur as universal at least once.

Rule 5. If both the premises are positive, the conclusion is positive.

Rule 6. If one of the premises is negative, the conclusion is negative.

Rule 7. One of the premises must be positive, otherwise, the syllogism is invalid.

Rule 8. One of the premises must be universal.

Rule 9. If one of the premises is particular, the conclusion is particular.

Rule 10: Nothing may be asserted in the conclusion which has not been asserted in the premises.



Reference: Maboloc, Christopher Ryan and Pascua, Edgar. 2008. Elements of Logic. Rex Bookstore: Manila, Philippines.