In chapter 9 of the Poetics Aristotle states that poetry is concerned with the universal. In this paper I shall consider three questions arising out of this statement. First, what does it mean? Secondly, what constraints does it impose on the construction of tragic plots? I shall consider this question with special reference to the possible role of chance in tragedy. Thirdly, why is poetry concerned with the universal – that is, why is poetry such that these constraints are appropriate?