We examine the proposition that, in ordinary conversation, people are concerned to argue - to justify their claims and to counter potential and actual counter claims. We test out the proposition by analysing explanations in one particular conversation. We attend to the validity claims of what the speakers say, and to the authority with which they say it. Viewed in that light, we find that the majority of what might look like causal attributions turn out to look like argumentative claim-backings. We then go on to flesh out the quasi-pragmatic rules which might help to decide formally whether any given utterance is be er understood as an argument or a causal explanation. These rules revolve around the speaker's apparent intention and the projected relationship between the clauses in what she or he says. All of this takes us a fair way from attribution theory's model of explanation as the reporting of a cause, and we end up with an argumentative model of ordinary explanation.