We present a metalogical characterisation of relevance for systems
of defeasible argumentation and use it to de¯ne the notion of a rele-
vant argument system. We employ a variant of the idea (in°uential
in linguistics and philosophy) that communication and cognition are
governed by a trade-o® between opposing demands of informational
su±ciency and economy of means; the notion of informational suf-
¯ciency is modelled in terms of satisfying a query associated with a
topic of argumentation, while the notion of economy is based on proof-
theoretic minimality. The resulting system of relevant argumentation
is able to handle fallacies of relevance, such as the paradoxes of ma-
terial implication, even when the underlying deductive system is a
classical rather than a relevance logic.