The Distribution of Terms in the 4 Categorical Propositions A, E, I, O - Ch. 5.4 in "The Reasonable Person" by Mark Grannis

Grannis begins this chapter reviewing the concepts of supposition which we learned in unit 2.4. There isn't really anything new here. The real meat of the chapter deals with the concept of distribution of terms. The distribution of terms refers to whether or not the whole extension of a thing is being spoken about, or only part. Grannis phrases it as: "A term is distributed in a proposition when the proposition addresses the entire extension of concept signified by the term." 

As far as the distributed or undistributed nature of the terms in the four basic categorical propositions: A, E, I, O, here is a summary from Grannis: "Subjects are distributed in universal propositions and undistributed in particular propositions. Predicates are distributed in negative propositions and undistributed in affirmative propositions." 

A Proposition: All S is P.

The subject is distributed but the predicate is undistributed. (This is because you are making a claim about all of the subject, but this statement isn't making a claim about all of the predicate.)

E Proposition: No S is P. 

The subject is distributed and the predicate is also distributed. (This is because you are making a claim about all of the subject and you are saying that it has no relation to all of the predicate.)

I Proposition: Some S is P.

The subject is undistributed and the predicate is also undistributed. (This is because you are not making a claim about all of the subject, nor are you making a claim about all of the predicate.) 

O Proposition: Some S is not P.

The subject is undistributed and the predicate is distributed. (This is because you are not making a claim about all of the subject, but the statement is saying something about the whole of the predicate, namely that the subject has no part of any of the predicate.)