In the Syllogism: "Man is mortal; Socrates is a man; therefore Socrates is mortal," we have the following arrangement: "Mortal," the Major Term; "Socrates," the Minor Term; and "Man," the Middle Term; as follows: _Major Premise_: "Man" (_middle term_) is mortal (_major term_). _Minor Premise_: "Socrates" (_minor term_) is a man (_major term_). _Conclusion_: "Socrates" (_minor term_) is mortal (_major term_). The reason for the rule that there shall be "_only three_" terms is that reasoning consists in comparing _two terms_ with each other through the medium of a _third term_. There _must be_ three terms; if there are _more_ than three terms, we form two syllogisms instead of one. III. _That one premise, at least, must be affirmative._ This, because "from two negative propositions nothing can be inferred." A negative proposition asserts that two things differ, and if we have two propositions so asserting difference, we can infer nothing from them. If our Syllogism stated that: (1) "Man is _not_ mortal;" and (2) that "Socrates is _not_ a man;" we could form no Conclusion, either that Socrates _was_ or _was not_ mortal. There would be no logical connection between the two premises, and therefore no Conclusion could be deduced therefrom. Therefore, at least one premise must be affirmative. IV. _If one premise is negative, the conclusion must be negative._ This because "if one term agrees and another disagrees with a third term, they must disagree with each other." Thus if our Syllogism stated that: (1) "Man is _not_ mortal;" and (2) that: "Socrates is a man;" we must announce the Negative Conclusion that: (3) "Socrates is _not_ mortal."