What's the Collective Cultural Grammar?

In the story, struthers and capelli are in a relationship that is founded on ths collective cultural grammar of telling the truth when you witness something. And we can look at beyond the surface stakes in terms of when does he differentiate from that collective cultural grammar, and when does he conform to it? So how would you classify that? Well, if he leaves, he differentiates, and if he stays, he conforms.