Concessions 'for the sake of argument'

When an agent A argues with another agent B that has its own (different) knowledge-base (i.e. different beliefs, desires, intentions, values, preferences etc) then the dialogue proceeds on the basis of publicly agreed matter. This publicly agreed matter are concessions taken on by both parties for the sake of progression of the dialogue/argument. Otherwise, if A presents an argument to B with premises not shared by B it may not be accepted.