Two beliefs were fundamental to Athenian moral thinking about war: first, starting a war without provocation was unjust and, second, states had a right to defend themselves. These judgments seem simple and familiar. When we examine the details of what counted as provocation, what it could justify, and how the argument for self-defense was deployed the picture becomes more complicated and more dependent on its specific historical and social context. We will examine condemnations of aggression in a variety of contexts, but here I will briefly preview a few of the relevant issues. I then turn to the elaborations of the argument for self-defense, the main subject of this chapter.

Despite the condemnation of unprovoked aggression, wars of self-defense were not the only type of just war: the Athenians did not believe in defensivism, the idea that only defensive wars were justified. Indeed, Athenian morality was offended as easily by staying at peace as by going to war: wars of revenge were perfectly just; staying at peace when an ally required support was morally indefensible. So one state might invade another's territory with complete justification. Unprovoked aggression, on the other hand, was generally condemned. It would only be a slight exaggeration to say that none of the moral argumentation of deliberative oratory makes sense without reference to this basic assumption: Why would Athenian orators justify a war if war required no justification? Why would they accuse rival states of aggression if aggression were not generally condemned?