Aristotle has just finished showing how related words can indicate a difference in meaning. Now he continues explaining the use of the second tool by discussing how predicates show a difference in meaning. He does this in Topics, Book 1.
Look also at the classes of the predicates signified by the term, and see if they are the same in all cases. For if they are not the same, then clearly the term is homonymous: e.g. good in the case of food is what is productive of pleasure, and in the case of medicine what is productive of health, whereas as applied to the soul it is to be of a certain quality, e.g. temperate or courageous or just; and likewise also, as applied to a man. Sometimes it signifies what happens at a certain time, as (e.g.) what happens at the right time; for what happens at the right time is called good. Often it signifies what is of a certain quantity, e.g. as applied to the proper amount; for the proper amount too is called good. So then good is homonymous. In the same way also clear, as applied to a body, signifies a colour, but in regard to a sound it denotes what is easy to hear. Sharp, too, is in a closely similar case; for the same term does not have the same use in all its applications; for a sharp note is a swift note, as the mathematical theorists of harmony tell us, whereas a sharp angle is one that is less than a right angle, while a sharp dagger is one cut at a sharp angle.
We should examine the various ways that this word we are investigating is applied to various subjects as a predicate. If it is applied to one subject and and means one thing, but when applied to a different subject means something else, then the word has multiple meanings. For example, when we apply the word ‘good’ to food, we sometimes mean that the food tastes good. On the other hand, when we apply the word ‘good’ to medicine, we mean that the medicine will help us become healthy. Since becoming healthy and tasting good are not the same, the word ‘good’ means different things. Nor are these the only meanings of good. Consider that a person is good if they have good character qualities such as justice, moderation and courage. Events are called good if they happen at the right time, or if there is the proper amount of something in a mixture. So good has many meanings. Another example is the word ‘clear’. When we call an object ‘clear’ we indicate that we can see through it, but a clear sound is one that is easy to hear.
Next, Aristotle discusses how the genera of things help to show differences in meaning.