Walter Carnielli , Marcelo E . Coniglio and João Marcos Logics of Formal Inconsistency

In traditional logic, contradictoriness (the presence of contradictions in a theory or in a body of knowledge) and triviality (the fact that such a theory entails all possible consequences) are assumed inseparable, granted that negation is available. This is an effect of an ordinary logical feature known as ‘explosiveness’: According to it, from a contradiction ‘α and ¬α’ everything is derivable. Indeed, classical logic (and many other logics) equate ‘consistency’ with ‘freedom from contradictions’. Such logics forcibly fail to distinguish, thus, between contradictoriness and other forms of inconsistency. Paraconsistent logics are precisely the logics for which this assumption is challenged, by the rejection of the classical ‘consistency presupposition’. The Logics of Formal Inconsistency, LFIs, object of this chapter, are the paraconsistent logics that neatly balance the equation: