ABSTRACT
Aristotelian logic occupied itself almost exclusively with the logical relations between sentences of the form 'Every A is/isn't a B' and 'Some A's are/aren't B's'. The inferences constructed out of these sentences were divided into three groups: the Square of Opposition, immediate inferences, and syllogisms. This chapter proves that all the logical relations of the Aristotelian Square of Opposition. Aristotelian logic classified as immediate inferences those inferences that have a single premise and in which the subject or the predicate of the conclusion are different from those of the premise. Four kinds of immediate inferences were recognized: conversion, obversion, contraposition and inversion. Syllogisms are inferences with two premises, in which the subject of the conclusion is either the subject or the predicate of one of the premises, the predicate of the conclusion is either the subject or predicate of the other premise, and both premises contain one more concept, the middle term, as either the subject or predicate of each.
