Look again at the four forms. Some of them say something about every member of a class; others speak about only part of it. A term is distributed in a proposition when the proposition says something about every member of the class it names.
| Form | Subject | Predicate |
|---|---|---|
| A: All S are P | distributed | not |
| E: No S are P | distributed | distributed |
| I: Some S are P | not | not |
| O: Some S are not P | not | distributed |
Key idea
Universal statements (A, E) distribute their subject. Negative statements (E, O) distribute their predicate. So A distributes S, E both, I neither, O only P.
Why it works
Take each form in turn. "All S are P" speaks of every S, but only of the P that happen to be S. "No S are P" shuts every S out of the whole of P, which says of every P that it is not an S: both terms. "Some S are P" speaks of at least one S and at least one P: neither class as a whole. "Some S are not P" speaks of only some S, but says that whole class P leaves those S out, so it tells us something about every P: the predicate.
Worked examples
Worked example: An A proposition
Which terms are distributed in "All dancers are musicians"?
- It is universal, so the subject dancers is distributed: it speaks of every dancer.
- It is affirmative, so the predicate musicians is not: it does not speak of every musician.
Answer: dancers only
Worked example: An O proposition
Which terms are distributed in "Some readers are not bakers"?
- It is particular, so readers is not distributed.
- It is negative, so bakers is distributed: every baker is outside the group of readers it mentions.
Answer: bakers only
Common mistake
Memorizing the chart without the reason, then forgetting the O form. "Some S are not P" excludes some S from all of P, so it speaks about every P. Check by asking, for each term, "Does this statement say something about every one of these?"