It is commonly thought that Thucydides died while still working on the History, since it ends in mid-sentence and only goes up to 410 BC, leaving six years of war uncovered. Furthermore, there is a great deal of uncertainty whether he intended to revise the sections he had already written. Since there appear to be some contradictions between certain passages in the History, it has been proposed that the conflicting passages were written at different times and that Thucydides' opinion on the conflicting matter had changed. Those who argue that the History can be divided into various levels of composition are usually called "analysts" and those who argue that the passages must be made to reconcile with one another are called "unitarians". This conflict is called the "strata of composition" debate. The lack of progress in this debate over the course of the twentieth century has caused many Thucydidean scholars to declare the debate insoluble and to side-step the issue in their work.
