Much work in the area of argumentation-based dialogues between agents has been based on the influential taxonomy of dialogue types developed by Walton and Krabbe. In this paper we re-examine the Walton and Krabbe framework, concentrating on the preconditions for different types of dialogue and analyzing them in a systematic way. Doing so identifies a number of new kinds of dialogue missing from the framework. We discuss some of the more interesting of these and develop protocols for them.