A Class Room Logic / Deductive and Inductive, with Special Application to the Science and Art of Teaching

by George Hastings McNair

An I proposition is converted simply only.

The O proposition does not admit of conversion.

(4) Immediate inference by contraversion is a process involving first obversion and then conversion.

“A,” “E” and “O” may be contraverted; “I” cannot be contraverted.

7. ILLUSTRATIVE EXERCISES.

(1a) From the antecedent judgment, “All weeds are plants,” I am able to derive by immediate inference these judgments: (1) “All weeds are not not-plants,” or “No weeds are not plants.” (2) “No not-plants are weeds.” (3) “Some plants are weeds.” (4) “Some weeds are plants.”

(1b) “All vertebrates have a backbone.” From the foregoing judgment derive immediately five different conclusions.

(2a) “All good citizens try to vote,”

“Albert White is a good citizen,”

Hence, “Albert White will try to vote.”