For a number of years, in the not too distant past, there was a lively debate between Plato's defenders and critics over the question of whether his Republic contained slaves. However, since the appearance of an article by Gregory Vlastos1 some twenty years ago, it seems to have been generally felt that the issue has been resolved, and the controversy has died down. Vlastos argued that the evidence admits of no doubt - Plato included slaves in his ideal state. In this paper, I wish to have the case reopened, and to revive interest in what I believe should continue to be a matter of debate. In opposition to what has become the standard view, I am inclined to think, on balance, that his Republic could not contain slaves. Vlastos begins by reminding us that, on those occasions when Plato wants to propose a radical change from existing institutions, he argues for such a change. If he had intended to abolish slavery from his ideal society, this would have been a radical change, and we should have expected him to indicate clearly such an intention, and to justify it. Since no justification is forthcoming, we may presume that no change is envisaged. This line of argument I shall call the presumptive argument. One version of it is mentioned by R. B. Levinson,2 namely that the rough and dirty work, carried on behind the scene by slaves, will take place as usual, and the continuance of slavery is assumed without question.