Abstract

In this paper the medieval octagons of opposition and equivalence are described and analized. One of them, the octagon for quantified predicates, is the simplest one and offers the pattern for the other two, the octagon for predicate with modal qualification and the octagon for quantified genitive and nominative sentences. Thus, the first is the princeps analogum for the other two, whose structure is more complex. Then we describe an internal square inside the octagon, the square of the so-called disparatae sentences, which obey no law from the traditional Aristotelian square.