Convertend.Converse.
All metals are elements.Some elements are metals.
All bees buzz.Some buzzing insects are bees.
All men are fallible.Some fallible beings are men.
All good teachers are sympathetic.Some sympathetic persons are good teachers.

The conclusions from the foregoing are these: First, the usual mode of converting an A is to interchange subject and predicate, limiting the latter by the word “some” or a word of similar significance. Second, this mode is called conversion by limitation. Third, the converse of an A is an I.

The Co-extensive A.

In the conversion of A propositions there is the one exception of “co-extensive A’s,” such as truisms and definitions. It will be remembered that with these both subject and predicate are distributed; hence, they may be interchanged without limiting the predicate by “some.” To illustrate: The converse of the truism, “A man is a man.” is “A man is a man,” while the converse of the definition, “A man is a rational animal,” is “A rational animal is a man.” This mode of interchanging subject and predicatewithout limiting the latter is called Simple Conversion. The ordinary A proposition is thus converted by limitation, while the co-extensive A is converted simply.

Converting an E proposition.

As both terms of the E proposition are distributed it is not possible to violate the rule of distribution. It is to be remembered that no fallacy is committed by “undistributing” a term which is already distributed.

Illustrations.

Convertend.Converse.
No men are immortal.No immortals are men. Simply.
No birds are quadrupeds.No quadrupeds are birds. Simply.
No metals are compounds.No compounds are metals. Simply.
No men are immortal.Some immortals (at least) are not men. Limitation.
No birds are quadrupeds.Some quadrupeds are not birds. Limitation.
No metals are compounds.Some compounds are not metals. Limitation.

Three facts are evident relative to the converting of an E. First: An E proposition may be converted either simply or by limitation. Second: E may be converted into either E or O. Third: If the converse is an O then is the inference a weakened one, being particular when it could just as well be universal.

Converting an I proposition.