We investigate Dung's semantics for assumption-based frameworks (ABFs) that are induced by contrapositive logics. We show that unless the falsity propositional constant is part of the defeasible assumptions, the grounded semantics lacks most of the desirable properties it has in abstract argumentation frameworks (AAFs), and that for simple definitions of the contrariness operator and the attacks relations, preferred and stable semantics are reduced to naive semantics. We also show the tight relations of this framework to reasoning with maximally consistent sets, and consider some properties of the induced entailments, such as being cumulative or preferential relations that satisfy non-interference.