A and E propositions are said to be universal propositions (because they are about all S), and I and O propositions are called particular propositions (because they are about some S). A and I propositions are described as affirmative propositions (because they say what is P), and E and O propo- sitions are referred to as negative propositions (because they say what is not P). Thus, these four basic propositional forms can be described this way:
A = Universal Affirmative E = Universal Negative
I = Particular Affirmative O = Particular Negative
These four forms fit into the following table:
Universal A: All S is P. E: No S is P.
Particular I: Some S is P. O: Some S is not P.
Here are the Venn diagrams for the four basic categorical forms:
S P S P
A: All S is P. E: No S is P.
I: Some S is P. O: Some S is not P.