Thought-Culture or Practical Mental Training

(E) _Universal Negative_: This form of proposition is converted by Simple Conversion. In a Universal Negative _both terms are distributed_. (“In universal propositions, the _subject_ is distributed;” “In negative propositions, the _predicate_ is distributed.”) So we may say “No cows are horses,” and then convert the proposition into “No horses are cows.” We simply convert one Universal Negative (E) into another Universal Negative (E).

(I) _Particular Affirmative_: This form of proposition is converted by Simple Conversion. For _neither term is distributed_ in a Particular Affirmative. (“In particular propositions, the _subject_ is _not_ distributed. In affirmative propositions, the _predicate_ is _not_ distributed.”) And neither term being distributed in the convertend, it must not be distributed in the converse. So from “Some horses are males” we may by Simple Conversion derive “Some males are horses.” We simply convert one Particular Affirmative (I), into another Particular Affirmative (I).

(O) _Particular Negative_: This form of proposition is converted by Contraposition or Negation. We have given examples and illustrations in the paragraph describing Conversion by Contraposition. The Particular Negative (I) is converted by contraposition into a Particular Affirmative (I) which is then simply converted into another Particular Affirmative (I).

There are several minor processes or methods of deriving judgments from each other, or of making immediate inferences, but the above will give the student a very fair idea of the minor or more complete methods.

_Exercise_: The following will give the student good practice and exercise in the methods of Conversion. It affords a valuable mental drill, and tends to develop the logical faculties, particularly that of Judgment. The student should _convert_ the following propositions, according to the rules and examples given in this chapter:

1. All men are reasoning beings. 2. Some men are blacksmiths. 3. No men are quadrupeds. 4. Some birds are sparrows. 5. Some horses are vicious. 6. No brute is rational. 7. Some men are not sane. 8. All biscuit is bread. 9. Some bread is biscuit. 10. Not all bread is biscuit.