  How do we know absences? I know that my glasses are not on the table but how? Dharmakīrti would answer, “By inference,” inferential knowledge of an absence being one of three fundamental types identified by the Yogācārin (see above). “If an elephant were in the room, I (S) would perceive it. I (S) do not perceive an elephant. Therefore, there is no elephant in the room”—similarly for my glasses not being on the table (presuming the table is not so cluttered that they could be concealed). Gautama and Vātsyāyana, without elaborating, agree that absences are known inferentially (Nyāya-sūtra 2.2.2). But Uddyotakara and the later tradition argue that we know absences sometimes perceptually. I cognize immediately my glasses’ absence when I look for them on the table.