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Philosophy Then

The Missing Link

Peter Adamson perceives absences in Indian epistemology.

I suppose we can all agree that it’s impossible to see something that isn’t there. But here’s a trickier question: can you see that something isn’t there? The director of a play may expect an actor to walk in on cue. If this fails to happen, the director will see, with great alarm, the absence of the actor. Or maybe you are told to fetch pieces of fabric from a pile, taking only those that have no mark on them. In this case you’d be looking for the absence of a mark on the fabric. And if you are looking for something, it had better be possible for you to see it.

This example was given by Gautama, author of the Nyāya-Sūtra, compiled in the first or second century AD. It is the founding text of Nyāya, an ancient Indian philosophical school that specialized in epistemology (also known as theory of knowledge). Central topics for Nyāya were the sources of knowledge, argument technique, the rules of debate, and the structure of logically valid arguments. This school was paired with Vaiśeṣika, a school whose remit was metaphysics. Together, the two schools explored what there is, and how we know about it.

Perception is important to Gautama and the later Nyāya tradition because, along with inference and testimony, it is identified as a fundamental ‘source of knowledge’ (pramāṇa). Since we rely on perception for knowledge, it must be shown to be reliable, even infallible, or, as Gautama puts it, that perception is ‘non-deviating’. It might seem that we sometimes make mistakes in perception, such as seeing a coiled rope and thinking it is a snake. But not unlike the ancient Greek Epicureans, the Nyāya hold that error comes in not with the raw perception, but at the stage where we apply concepts to what we perceive. We perceive the coiled rope to look how it really does look; the problem comes only when we conceive that something that looks like this is a snake.

This same example can be used to illustrate Gautama’s claim about absences. Suppose you think you see a snake coiled up in the corner. Upon further inspection, you realize with relief that it is only a rope. Here you are seeing the absence of the snake ‘in’ the rope, just as you can see the absence of a mark on an unmarked piece of fabric.

A Buddhist philosopher named Dharmakīrti denied this. He argued that you are not perceiving absences in such cases, but simply failing to perceive the relevant thing. So your knowledge that the thing is absent is (again) not a matter of perception, but of inference, the inference being, “Since I do not see a snake, there is no snake here (thank goodness).” But the Nyāya and Vaiśeṣika schools held fast to their claims, with later Vaiśeṣika texts even adding that absences are real properties that inhere in things, much like colors or other positive features.

Dharmakīrti’s objection sounds pretty plausible. So why did these philosophers insist that we can perceive absences?

Well, their claim would have come in very handy in the context of the Nyāya theory of reasoning, which was designed to explain how we establish a link between things and the features they possess. The classic example is seeing smoke on a mountain and reasoning on this basis that there is fire on the mountain, because where there is smoke, there is fire.

Gautama and his followers say that to establish such a conclusion, we should appeal to analogous cases: in the past you saw smoke in the kitchen, and there was fire in the kitchen too. Here smoke is the sign of the presence of the thing we are interested in, namely fire. We can also support the conclusion by referring to a negative case that’s not analogous. We might point out that there is no smoke in the kitchen when no one is cooking. The absence of smoke is a sign that fire is likewise absent.

Now we can see why it would make sense for the Nyāya to insist that we can perceive absences. Such cases are not supposed to be inferences themselves, but perceptions that license us to make inferences. The director’s seeing the absence of the actor onstage is the basis for her inferring that something has gone badly wrong; your seeing the absence of smoke in cases where there is no fire buttresses your conviction that smoke and fire always come together. Perception of absence can also help us with counterfactual reasoning. If my house were on fire, I would see smoke, so my seeing the absence of smoke is evidence that my house is thankfully not ablaze.

The larger purposes of Nyāya are, then, well-served by their claim about perceiving absences. But is that claim convincing?

To me it seems plausible to say that different kinds of perception are directed towards different kinds of objects: you see color, hear noise, smell scents, and so on. In each case the object will be some positive reality, not an absence. So I tend to think Dharmakīrti had a good point in arguing that ‘seeing’ an absence is just failing to see. Aristotle said something similar, namely that we can ‘see’ darkness only in a derivative sense, by noting that we are in fact failing to see anything. Furthermore, at any given time, an unlimited number of things are absent from my immediate environment: hippos, UFOs, European royalty, etc etc. Obviously I am not perceiving all these absences. So if I can really perceive an absence, it would have to be the absence of something I thought might be there and do not find. That pushes me in the direction of thinking that some sort of inference is indeed involved. But perhaps I’m just failing to see the point.

Peter Adamson is the author of A History of Philosophy Without Any Gaps, Vols 1-5, available from OUP. They’re based on his popular History of Philosophy podcast.