Note 26 — Chapter XXIII

For those who would make a further study of the syllogism the following rules are given: 1. In a syllogism there should be only three terms. 2. Of these three only one can be the middle term. 3. One premise must be affirmative. 4. The conclusion must be negative if either premise is negative. 5. To prove a negative, one of the premises must be negative.

Summary of Regulating Principles: 1. Terms which agree with the same thing agree with each other; and when only one of two terms agrees with a third term, the two terms disagree with each other. 2. "Whatever is affirmed of a class may be affirmed of all the members of that class," and "Whatever is denied of a class may be denied of all the members of that class."