Aristotle has just discussed how we can determine the truth of a predicate by examining the various species of the subject. He continues his discussion on universal predicates by showing that definitions can also help. He does this in Topics, Book 2.
Another rule is to make accounts both of an accident and of its subject, either of both separately or else of one of them, and then look and see if anything untrue has been assumed as true in the accounts. Thus (e.g.) to see if it is possible to wrong a god, ask what is to wrong? For if it be to injure deliberately, clearly it is not possible for a god to be wronged; for it is impossible that God should be injured. Again, to see if the good man is jealous, ask who is the jealous man and what is jealousy. For if jealousy is pain at the apparent success of some honest person, clearly the good man is not jealous; for then he would be bad. Again, to see if the indignant man is jealous, ask who each of them is; for then it will be obvious whether the statement is true or false; e.g. if he is jealous who grieves at the successes of the good, and he is indignant who grieves at the successes of the evil, then clearly the indignant man would not be jealous. A man should substitute accounts also for the words contained in his account, and not stop until he comes to something familiar; for often when the account is given as a whole, the point at issue is not cleared up, whereas if for one of the words used in the account an account be stated, it becomes obvious.
There is a way to determine whether or not an accident is possibly true of a thing. We must ask what the predicate and subject are. We do this by asking for definitions. We then compare the definitions with the predication to determine if something false has been assumed. For example, is it possible for a god to be abused? Well, if abuse is a kind of intentional harm, then God cannot be abused because he cannot be harmed. Another example is this: is the good man jealous? Well, if jealously is pain at the success of an honest person, then no good man can be jealous. If he were, then he would be a bad man rather than a good man. Or consider whether or not an indignant man could be jealous. If jealously is sadness because of the success of good people and indignant people are sad at the success of evil people, then it is not possible for the jealous person to be indignant. We can also substitute definitions for the words defined by the definitions. Continue to do this until you know what all of the words mean. This will make it obvious whether or not the accident is possibly true or not.
Next, Aristotle discusses a personal way to test universal predicates.