Book VII describes a point at which Plato's future rulers have completed their philosophical education. At that point they have a complete grasp of evaluative concepts (esp. of good), in that they can articulate and defend defi nitions of them against all objections. Immediately, without further training, they are charged with applying these concepts in their city. By contrast, Aristotle's ethical and political writings do not envisage any such point. This difference between Plato and Aristotle is no expository accident, but refl ects a fundamental disagreement between their respective views of the relationship between grasping and applying concepts, especially evaluative concepts. Aristotle's view is importantly similar to Wittgenstein's later view of 'how to go on' using a word 'in the same way'. This paper explores some aspects of this similarity between Aristotle's and Wittgenstein's opposition to platonism.