 A joint commitment is not a composite of two or more personal commitments. It is a commitment of two or more persons by two or more persons. [. . . .]  In order to create a new joint commitment each of the would-be parties must openly express to the others his readiness together with the others to commit them all in the pertinent way. Once these expressions are common knowledge between the parties, the joint commitment is in place—as they understand. Each is therefore now committed to do what he can to promote satisfaction of the joint commitment in conjunction with the actions of the rest. (Gilbert 2011: 92–3)