Aristotle has just finished explaining that differences in predicate meaning will show a difference in the meaning of a word. He continues his discussion of the second tool by showing that generic differences will also do this. He does this in Topics, Book 1.
Look also at the genera of the objects denoted by the same name, and see if they are different without the one falling under the other, as (e.g.) donkey is both the animal and the engine. For the account of them that corresponds to the name is different- for the one will be declared to be an animal of a certain kind, and the other to be an engine of a certain kind. If, however, the genera are subordinate one to the other, there is no necessity for the accounts to be different. Thus (e.g.) animal is the genus of raven, and so is bird. Whenever therefore we say that the raven is a bird, we also say that it is a certain kind of animal, so that both the genera are predicated of it. Likewise also whenever we call the raven a winged two-footed animal, we declare it to be a bird- in this way, then, as well, both the genera are predicated of raven. But in the case of genera that are not subordinate one to the other this does not happen- for whenever we call a thing an engine, we do not call it an animal, nor vice versa.
Look also and see not only if the genera of the term before you are different without being subordinate one to the other, but also in the case of its contrary- for if its contrary is used in many ways, clearly the term before you is as well.
Look at the genera that the term indicates and check to see whether they are the same genera. If not, then is one genera the genera of the other. If not, then the words have different meanings. Aristotles example of a donkey depends on Greek again, and the English language does not work that way. Our example might uncover the difference in the word rock. We can call a stone on the beach a rock, but we can also call a kind of music rock. Music is not the same thing as stones. Stones are not a kind of music, and music is not a kind of stone. Therefore, rock has multiple meanings. If music were a kind of stone or stones were a kind of music, then we could not say that rock had different meanings.
We must also check to see whether or not the contrary of the two genera is the same. If it is not, and one genera is not a kind of the other genera, then the word has multiple meanings.
Next, Aristotle discusses how definitions can show multiple meanings.