Some​ ​propositions​ ​are​ ​not​ ​only​ ​true,​ ​but​ ​could​ ​not​ ​have​ ​been​ ​otherwise. This​ ​thesis​ ​is​ ​about​ ​modality​ ​and​ ​the​ ​philosophy​ ​of​ ​language.​ ​Its​ ​centrepiece​ ​is​ ​a​ ​new​ ​account​ ​of the​ ​conditions​ ​under​ ​which​ ​a​ ​proposition​ ​is​ ​necessarily​ ​true​ ​in​ ​the​ ​above​ ​sense.