My object in this paper is to discuss not so much why the Peloponnesian War occurred (though I have views on that question, which will become apparent), but why Thucydides wrote as he did about why the war occurred.The problem is notorious. Every student knows that Thucydides mentions four immediate causes but judges them less important than one underlying cause2, yet an analysis of book I shows that different views of the causes of the war seem to be given side-by-side throughout