 Indeed, it was only in the 12th century, with Abelard, that a novel and highly sophisticated theory of consequence/entailment was to be formulated. Abelard’s starting point is the same material inherited from Boethius which had been available for centuries, and yet what he does with it is quite extraordinary; in particular, he understood better than anyone before him the nature of what we now refer to as propositional operations. His treatment of the conditional and of the disjunction echoes what is now known as connective logic (Martin 2018) (see entry on connective logic of this encyclopedia). And yet, his account is ultimately untenable, as the resulting system is in fact inconsistent (Martin 2004) (Martin 2018).