Aristotle has just finished describing what the second tool of argument is. Now he will continue explaining the various tools of argument by talking about how a difference in names can indicate a difference in meaning. He does this in Topics, Book 1.
Whether a term is used in many ways or in one only, may be considered by the following means. First, look and see if its contrary is used in many ways, whether the discrepancy between them be one of kind or one of names. For in some cases a difference is at once displayed even in the names; e.g. the contrary of sharp in the case of a sound is flat, while in the case of a body it is dull. Clearly, then, the contrary of sharp is used in many ways, and if so, so also is sharp; for corresponding to each of the former terms the contrary will be different. For sharp will not be the same when contrary to dull and to flat, though sharp is the contrary of each. Again that in the case of a sound has sharp as its contrary, but in the case of a body raised, so that that is used in many ways, inasmuch as its contrary also is so used. Likewise, also, fine as applied to an animal has ugly as its contrary, but, as applied to a house, mean; so that fine is homonymous.
The first way of determining whether or not a word is used in one way or many ways is by considering whether the contrary of that word is a different word in some cases. Sometimes it is and we know right away that the word has more than one meaning. For example, the word ‘sharp’ has more than one meaning that can be discovered this way. A ‘dull’ knife is the contrary of a ‘sharp knife, but a ‘flat’ sound is the contrary of a ‘sharp’ sound. Since dull and flat are different words, they indicate that sharp has a different meaning in these cases. So ‘sharp’ means one thing when we are speaking of physical objects and another thing when we are speaking of sounds. Aristotle also applies this example to our description of animals. This is to show that sometimes the different meanings are similar to each other even though they are not the same. The word ‘fine’ is an example of this. An ‘ugly’ animal is the contrary of a ‘fine’ animal, but a ‘mean’ horse is the contrary of a ‘fine’ horse. So fine has more than one meaning that are each similar to the other.
Today, this test is still used in semantics to test whether or not words are similar in meaning. However, we now call words that have similar meanings but identical spellings polysemous.
Next, Aristotle discusses how some terms have identical contraries but are still obviously different in kind.