  For the relevant logic \(\mathbf{R}\) and its interpretation of natural language conditionals, more work must be done in identifying what features of reality the formal semantics models. This has been a matter of some controversy, since not only is the ternary relation unfamiliar to those whose exposure is primarily to modal logics with a simpler binary accessibility relation between possible worlds, but also because of the novelty of the treatment of negation in models for relevant logics. It is not our place to discuss this debate in much detail here, Some of this work is reported in the article on  relevant logic  in this Encyclopedia, and a book-length treatment of relevant logic in this light is Mares’ Relevant Logic: a philosophical interpretation (2004).