Aristotle has just finished talking about how intermediate words can indicate a difference in meaning. Now he will continue his discussion of the second tool by explaining how a difference in contradictories indicates a difference in meaning. He does this in Topics, Book 1.
Again, in the case of the contradictory opposite, look and see if it is used in more than one way. For if it is, then the opposite of it also will be used in more than one way; e.g. to fail to see is used in more than one way, viz. to fail to possess the power of sight, and to fail to put that power to active use. But if this is used in more than one way, it follows necessarily that to see also is used in more than one way; for there will be an opposite to each way of failing to see; e.g. the opposite of failing to possess the power of sight is to possess it, while of failing to put the power of sight to active use, the opposite is to put it to active use.
Consider the contradictory of the word you are looking at. If the contradictory is used in a different ways in different contexts, then the word means something different. This is because the opposite of the a contradictory is the word under consideration. An example of this is the verb ‘to see’. Failing to see is used in more than one sense. People point out that they did not see something and mean that they did not notice it. They also use the word to indicate blindness. Therefore, the word ‘to see’ can mean to notice or to have the power of sight.
Next, Aristotle will discuss how privations and possession show differences in word meaning.