Distribution of Terms in A, E, I and O

In one line

A term is distributed in a proposition when the proposition says something about every member of the class that term names.

In the wording a student can write in an examination: a term is said to be distributed when it is used in its full extension, that is, when the proposition refers to all the members of the class denoted by it; and undistributed when it refers to only part of that class.

The idea, before the table

Take "All contracts are agreements."

What does it tell you about contracts? Everything: it speaks of every single contract. The subject term is used in its full extension. It is distributed.

What does it tell you about agreements? Very little. It says that contracts are among the agreements. It says nothing about the agreements that are not contracts, and there are many. The predicate term is used of part of its class only. It is undistributed.

That is the whole idea, and it can be tested on any proposition with one question: does this proposition tell me something about every member of the class this term names? If yes, distributed. If no, undistributed.

The four propositions, worked

A: All S is P. "All contracts are agreements."

Subject: distributed. Every contract is spoken of.

Predicate: undistributed. Nothing is said about agreements generally, only that the contracts are among them.

E: No S is P. "No minor's agreement is enforceable."

Subject: distributed. Every minor's agreement is spoken of, and each is excluded from the predicate class.

Predicate: distributed. This is the one people find surprising, and the reason is worth working out. To say that no minor's agreement is enforceable is to say that of every enforceable thing, none is a minor's agreement. The whole of the predicate class has been swept and every member of it excluded from the subject class. A negative proposition necessarily says something about the entire predicate class, because exclusion is total in a way inclusion is not.

I: Some S is P. "Some agreements are contracts."

Subject: undistributed. Only part of the agreements is spoken of.

Predicate: undistributed. Only part of the contracts is spoken of.

O: Some S is not P. "Some agreements are not contracts."

Subject: undistributed. Only part of the agreements is spoken of.

Predicate: distributed. Again the negative does it. To say that some agreement is not a contract is to say that this agreement is excluded from the whole of the class of contracts, every one of them, so the predicate class is spoken of in its entirety.

The table, and the two rules that generate it