│ │ │ is S (I) │ O and conversion of I. * – Name of proposition † – “S” represents any subject and “P” any predicate. INFERENCE BY INVERSION. Some logicians treat of a form of immediate inference known as inversion though it is of small importance and of little practical value. The process can be applied only to propositions A and E. In the one case the _contradictory subject_ is limited by “_some_” and then denied of the predicate, whereas, in the other case, the contradictory subject is merely affirmed of the predicate. _Illustrations._ _The Given Proposition._ _The Inverse._ I. All S is P. (A) Some not-S is not P. (O) All planets rotate. Some not-planets do not rotate. II. No S is P. (E) Some not-S is P. (I) No men are immortal. Some not-men are immortal. From the foregoing we are able to conclude _that the inverse of “A” is found by negating the subject and changing to an “O”; while the inverse of “E” is found by negating the subject and changing to an “I.”_ =5. OUTLINE.= IMMEDIATE INFERENCE――OPPOSITION――OBVERSION, CONVERSION, CONTRAVERSION AND INVERSION. 1. The Nature of Inference. 2. Immediate and Mediate Inference. 3. The Forms of Immediate Inference. (1) Opposition. (a) Scheme of Opposition. (b) Square of Opposition. (2) Obversion. (3) Conversion. (a) Simply. (b) By Limitation. (4) Contraversion. Inversion. =6. SUMMARY.= 1. Inference is the thought process of deriving a judgment from one or two antecedent judgments. 2. Immediate inference is inference without the use of a middle term. Mediate inference is inference by means of a middle term. 3. The four common forms of immediate inference are (1) opposition, (2) obversion, (3) conversion, (4) contraversion. (1) The name _opposition_ stands for certain definite relations which exist between the logical propositions when they are given the same subject and predicate. The one principle underlying opposition is: Whatever is said of the entire class may be said of a part of that class. The two statements which sum up opposition are first, an I may be derived from an A; and second, an O may be derived from an E. The crucial fact made obvious by the square of opposition is that A and O are mutually contradictory; likewise E and I. (2) Obversion is the process of passing from an affirmative to its equivalent negative or from a negative to its equivalent affirmative. “Two negatives are equivalent to one affirmative,” is the basic principle of obversion. The proposition A may be obverted by negating the predicate and changing to an E. “E” is obverted by negating the predicate and changing to an A. “I” is obverted by negating the predicate and changing to an O. “O” is obverted by negating the predicate and changing to an I.