Rule 2: The transitory term must be “distributed” (i.e., universal) in at least one premise (either the major premise or the minor premise).
Under this Rule, the middle term must describe the entire class contained within either the major premise or the minor premise. Otherwise, each term in the conclusion could be connected to some different part of the class that was not included within the premise statement, thus preventing the conclusion from stating a categorical truth. To illustrate this concept, consider the following example:
(1)   All Greeks (major term) are men (transitory term).

(2)   All Persians (minor term) are men (transitory term).

(3)   Therefore, all Greeks are Persians.

greek socrates guy egyptian guy holding tablet

Here, although both the major and the minor premises are true, the conclusion is obviously not valid. The reason for this is that the transitory term (men) as used in BOTH premise statements is NOT universal. The transitory term (men) is not “distributed” in either premise statement. That is, in this example neither the major nor the minor premise encompasses the entire class of men. Thus, Rule 2 is violated because both premise statements describe something less than the full class of men. Any logical comparison between only partial classes (i.e., the class of all Greeks and the separate class of all Persians) cannot produce a categorically valid conclusion as to the entire class that consists of ALL men).