When Kraut argues that, for Aristotle, the standards of proof are not lower than in other disciplines, he uses a passage from J.S. Mill's Utilitarianism as an example of the contrary view. And yet in that passage Mill is putting forward a view shared by Aristotle! This seems an unaccountable gaff in what is otherwise an accurate and reliable essay.
Kraut says the following:
It might be thought that in ethics proof (as we use that notion) is simply not possible, and that moral philosophy is never entitled to use that word about what can be achieved by even the best methods...According to Kraut, Mill is expressing here the view that the "level of justification is lower [about practical matters] than is available in other matters."
Someone who thinks that ethics is circumscribed in this way will find some support for his view in a well-known passage near the end of the first chapter of John Stuart Mill's Utilitarianism. Speaking of his "Utilitarian or Happiness theory," he says that he will give "such proof as it is susceptible of," but then adds immediately: "It is evident that this cannot be proof in the ordinary and popular meaning of the term. Questions of ultimate ends are not amenable to direct proof. Whatever can be proved to be good, must be so by being shown to be a means to something admitted to be good without proof."
But this is a simple misinterpretation. In the passage (and see the beginning of chapter 4, too, for further confirmation) Mill is not drawing a contrast between 'practical matters' and 'other matters'. His contrast is rather between 'ultimate principles' and 'derived principles', and he is making the thoroughly Aristotelian point (see Metaphysics IV.4) that ultimate principles do not admit of direct proof.
So Kraut quotes Mill in illustration of a view supposedly opposed to Aristotle, referring to a passage in which Mill--certainly, and rightly--would have thought himself to be echoing a familiar Aristotelian doctrine!