We must have a time coordinate, in view of tensed sentences and such sentences as 'Today is Tuesday'; a place coordinate, in view of such sentences as 'Here there are tigers'; a speaker coordinate in view of such sentences as 'I am Porky'; an audience coordinate in view of such sentences as 'You are Porky'; an indicated objects coordinate in view of such sentences as 'That pig is Porky' or 'Those men are Communists'; and a previous discourse coordinate in view of such sentences as 'The aforementioned pig is Porky'.