FIGURE II.
§ 610. Proof of Rule 1,—One or other premiss must be negative.
A—B C—B C—A
The middle term being predicate in both premisses, one or other must be negative; else there would be undistributed middle.
§ 611. Proof of Rule 2.—The conclusion must be negative.
Since one of the premisses is negative, it follows that the conclusion also must be so (by Rule 6).
§ 612. Proof of Rule 3.—The major premiss must be universal.
The conclusion being negative, the major term will there be distributed. But the major term is subject in the major premiss. Therefore the major premiss must be universal (by Rule 4).