This chapter talks about the notion of logical necessity. Only as a consequence of holding a philosophical theory would a person say that all six propositions are empirical; and if asked, away from the heat of metaphysical debate, to pick out those propositions in the set which are logically necessary, even he would be able to do so quite easily. For the concepts of logical necessity, entailment, logical impossibility, and are relatively simple by comparison with many concepts outside of philosophy which have, either partly or wholly, been successfully analysed. The chapter argues against the views as if they are the false results of incorrect analyses of the concept of logical necessity, then proceeds to an attempt to analyse the concept, and concludes with a hypothesis according to which the philosophical theories are not theories in the usual sense, that is, in the sense in which a theory explains a phenomenon and is either true or false.