Logical Studies

Abstract One of the methods of immediate inference in logic is the conversion. Logicians have identified three types of conversion: conversion, obverted contraposition, and contraposition. The present study, by means of a dichotomous division demonstrates that a further valid and new type of conversion can be posited which has been overlooked by logicians. In this newly identified form, after the conversion of subject and predicate, only the subject is complemented, in such a way that, assuming the truth of the original proposition, the converted proposition is likewise true. This study names this newly identified type “complemented subject conversion” and establishes its logical variations due to the various forms of categorical propositions, whether predicative or conditional. Accordingly, the complemented subject conversion of affirmative propositions (both universal and particular) yields a particular negative proposition, while in the case of a universal negative proposition, it’s a universal affirmative proposition. Particular negative propositions have no valid complemented subject conversion. By employing this innovative type of conversion, a greater number of true propositions can be inferred and derived from a given true proposition, which endows it with a logical value comparable to that of the other recognized types of conversion.