Term-negation may preface either or both terms. We need in our symbolism also ways of representing connections between propositions. The square of opposition and immediate inference fall under the first heading, syllogisms and polysyllogisms under the second. The square of opposition depicts various kinds of 'opposition' between the four propositional forms. Immediate inference , which consists in drawing a conclusion from a single premiss, encompasses conversion, obversion, contraposition, and inversion.
Conversion consists in reversing the order of terms.
I ba are called conversion per accidens . Obversion consists in negating the second term of a proposition and changing its quality. Contraposition consists in negating both terms and reversing their order. O nbna . Inversion consists in inferring from a given proposition another having for its subject the negation of the original subject.