Here it may be well to explain that when reference is made to subject or predicate the _logical_ subject or predicate is meant. Unless this is constantly kept in mind error results; e. g., in the proposition, “All white men are Caucasians,” the logical subject is “white men,” not “men.” If the subject were “men,” it would be undistributed, as the whole of the man family is not considered, but the actual subject, being “white men,” _is_ distributed because the predicate refers to _all_ white men.
Recurring to the illustration, “All men are mortal,” we have concluded that the subject “all men” is distributed. The predicate, “mortal,” however, is undistributed, as reference is made to it only in part; i. e., there are other beings aside from men that are mortal, such as “trees,” “horses,” “dogs,” etc. _In all A propositions of the type of “all men are mortal,” the subject is distributed while the predicate is undistributed._ This relation is clearly shown by the diagrammatical illustration, Fig. 1. Here _all_ of the “men” circle is identical with only a part of the “mortal” circle. In other words, the _whole_ of the “men” circle is considered, while reference is made to only a _part_ of the “mortal” circle.
_In the case of the co-extensive A both subject and predicate are distributed._ Relative to the co-extensive “All men are rational animals,” it could likewise be said that “all rational animals are men,” or that “all men are all of the rational animals.” Reference is thus made to _all_ of the definite predicate as well as to all of the definite subject.
In the E propositions, such as “No men are immortal,” the whole of the subject is excluded from the whole of the predicate. This makes evident the fact that _both terms are distributed_. See Fig. 2.
The I proposition, such as “Some men are wise,” concerns itself with only a part of the subject and only a part of the predicate, _consequently neither subject nor predicate is distributed_. This relation is verified by the representation, Fig. 3.
_In the O proposition the subject is undistributed, while the predicate is distributed._ For example, in the proposition, “Some men are not wise,” “some men” would indicate that only a part of the logical subject is under consideration. But the predicate is distributed because “some men” is denied of the _whole_ of the predicate, “wise.” This may become clear by studying Fig. 4. Here all of the shaded part which stands for the subject, “some men,” is excluded from the whole of the “wise” circle. But all of the shaded part is only a part of the entire “men” circle, consequently the subject which the shaded part represents (some men) is undistributed. The predicate, “wise,” however, is distributed, as the subject is excluded from every part of it. It is well to remember that _not_, when used with the copula, distributes the predicate which follows it.