DIAGRAM
1

R. Ishmael’s Rule No. 1,
concerning a-fortiori argument, can be represented by a triangular
star, at the center of which is the middle item (R) through which the three
other items, P, Q, and S are related to each other.

Diagram 1a

The a-fortiori
argument may also be represented, with reference to the comparative propositions
that underlie it, as ordering items P, Q, and S, according to their position in
a common continuum R:

Diagram
1b

This diagram is based on the following syllogisms:

Note that the four figures of a-fortiori should not be confused with the
four of syllogism they imply, which are, in the order shown: the fourth, third,
first and second figures.