Aristotle has just finished discussing how to use various propositions in arguments. Now he continues his discussion of the various tools of argument by introducing the second tool. He does this in Topics, Book 1.
On the subject of propositions, the above remarks are enough. As regards the number of ways in which a term is used, we must not only treat of those terms which are used in different ways, but we must also try to render their definitions– e.g. we must not merely say that justice and courage are called good in one way, and that what conduces to vigour and what conduces to health are called so in another, but also that the former are so called because of a certain intrinsic quality they themselves have, the latter because they are productive of a certain result and not because of any intrinsic quality in themselves. Similarly also in other cases.
Now Aristotle is finished discussion of the first tool propositions. When words are used in different ways, we cannot merely find out what these different ways of using words are. We must also find out everything about why these words are used differently. For example, justice and courage are both good in one way while whatever makes us healthy is good in a different way. If we are trying to understand what good is, then we cannot merely show that it is used in different ways. We also have to find out why it is used in different ways. Justice and courage are both good because they have something good. Whatever makes us healthy is good because it makes us healthy, not because of something good it has. We must analyze all other terms in a similar fashion.
This is the reason why philosophy is not merely arguments about words. We want to know why are words mean different things because these different things are different things in the world not merely in our words.