Immediate Inference:
Conversion

The converse of a proposition is the result of switching its subject and predicate terms.

Example:

The converse of the I proposition, "Some Englishmen are Scotch drinkers" is "Some Scotch drinkers are Englishmen"--another way of saying the same thing. If the first proposition is true, the second must be true, and vice versa.

The converse of "No women have been U.S. presidents" is "No U.S. presidents have been women." Once again, the statements are equivalent.

It is not legitimate to take the converse of an A proposition. The converse of "All pickpockets are criminals" would be "All criminals are pickpockets." As you can see, the converse here is not equivalent--the first proposition is true, but its converse is false.

Finally, let's look at the O proposition. An O proposition is not logically equivalent to its converse. "Some human beings are not Americans" does not imply "Some Americans are not human beings."

Converse is legitimate only for E and I propositions. Notice that these are propositions in which the subject and predicate terms have the same distribution value--either both are distributed, as in E, or both are undistributed, as in I.


Conversion | Obversion | Contraposition

Immediate Inference

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