To use the above scheme, read horizontally from left to right. For example: If A be true, then all in the row opposite obtains; that is, A is true, E is false, I is true, and O is false. (We take it for granted that the student will see that the first column belongs to A, the second to E, the third to I, and the fourth to O.) If E be true, then A is false, E is true, I is false, O is true, etc.
The whole of opposition is comprehended in two facts which are based upon one principle. This is the principle: Whatever may be said of the entire class may be said ofa part of that class. To put it in another way: Whatever is affirmed of all may be affirmed of some, or, Whatever is denied of all may be denied of some. To illustrate:
Accepted truth: All planets rotate. (A)
Accepted inference: Some planets rotate. (I)
or
Accepted truth: No planet is a sun. (E)
Accepted inference: Some planets are not suns. (O)
These are the two facts: First, a particular affirmative may be derived from a universal affirmative. Second, a particular negative may be derived from a universal negative. Or, more briefly: An I may be derived from an A, and an O from an E.
SQUARE OF OPPOSITION.