The Sutra says that opponents argue that objects are like dreams, mirages, or magic cities in the sky, not fixed as real, and says that they haven’t provided a reason to accept this. Vatsyayana says when we wake, we see with perception that the dreams weren’t real, which shows us perception and illusion are different. A Buddhist could object that they are making a comparison, a valid source of knowledge. The Nyaya would argue that perception is primary and more certain than comparison, such that physical objects are like mirages, but not entirely, as they are better established. But how can we say this without making a comparison to check, just as we are checking perception against comparison, with comparison, right now?
The Nyaya Sutra says that words are used to refer in three ways, to individuals, forms, and classes, and these multiple ways produce doubt, which sparks inquiry. (2.2.59) Vatsyayana provides us with the example of cow, and says the word refers to an individual cow, and anything shaped like a cow (to use the word metaphorically, as cow-ish-ness), and the class of all cows, which the Nyaya argue all have horns and four legs, like other classes of animals, forms of animals and individual animals. Vatsyayana says that the object of the word is thus determined by our ability to use it in these ways. The Sutra refutes those who think words refer to only one of these things, simply individuals, or simply forms, or simply classes, and says the meaning of a word is clearly all three of these uses. The Sutra uses the example of a clay cow, which has the form of a cow, and is included in classes such as things that have four feet, like a cow, but as Vatsyayana adds, if someone says to wash, bring or donate a cow, and we hand them a clay cow statue, we are wrong, and do not satisfy their requests, as it lacks the category of being alive, or an animal at that, so it is certainly the wrong sort of individual.