Gautama and the Nyaya base their entire system, which they argue, like the world, is a coherent, positive whole, on one source of knowledge, perception, as the Charvakas do, but they also argue that there are three other sources of knowledge that serve as bases for justifiable positions, beliefs and arguments, inference, as do the Vaisheshika, but also comparison (which some translate as analogy, an extensive comparison) and testimony, like the evidence of a witness in court for something we didn’t see. Thus, there are four sources (pramana) of knowledge for the Nyaya, but the later three are secondary and inferior to the first, direct experience of what we infer, compare or hear about through testimony of others.
The word pramana, which the Nyaya use for source, foundation, or evidence, means proof, and comes from the word roots for out from (pra) and measurement (ma), such that measuring out things to judge them is talking things out in debate. The Buddhists refer to it as pramanavada, the way or viewpoint of measuring things out. The Nyaya argue a proper understanding of the inventory of reality is important to act effectively, assuming reality has an order independent of our minds and cultural practices. Vatsyayana, the foremost Nyaya logician after Gautama, says that all of the Nyaya method is investigation of subjects by means of sources, and Uddyotakara says the best reasoning involves many sources to establish a position well.
The Nyaya lean towards “innocent until legitimate doubt” about belief, which means they lean towards positive belief, unless things are disproven or there is some evidence against them. Inferences can be hastily drawn, but if they are drawn slowly, based in good, careful reason, we should entertain them positively and favorably, not as certain but as openly possible. The same is true of perception, comparison and testimony, such that they are overall reliable, if we are careful with them. If a belief that exists is doubtable, we should investigate it with sources and testing possibilities, using hypothetical reasoning (tarka). The Charvakas, Buddhists, and other skeptics doubt that conviction and coherence is what we need as opposed to tranquility and perspective. In the beginning of Vatsyayana’s commentary on the Nyaya Sutra, he argues:
When things are grasped through sources of knowledge (pramana), it is possible to act and succeed. Thus, sources of knowledge are useful (arthavat). Without sources of knowledge, there would be no successful action… Success is a relationship with its result: gaining or losing things, which could be happiness or sadness, or some way to or from either. The ends served by sources of knowledge are innumerable, since the living things who use sources of knowledge are themselves innumerable.
When sources of knowledge are connected to things, so are the knower, known and knowledge. Why? Because without all of these knowledge of things is impossible. Of these, the person who acts with desire or fear is the knower, the way it is known is the source of knowledge, the known is the object, and truthful thought made the right way is knowledge. Truth is fully grasped when these four are in place.
So, what is truth? It is the grasping of being in something that is and not-being in something that isn’t. Grasping what is as what is, and what isn’t as what isn’t, is truth, as it is, unchanging.
How can something that isn’t be grasped through a knowledge source? At the time something that is is grasped, there is not grasping something that isn’t, like the light of a lamp that shows something that is and so also what isn’t. We think, if it was there, it would have been seen, but it wasn’t seen, so it isn’t there.
In Through The Looking Glass, Alice tells the White King she sees no one on the road, and the king praises her for having such eyes, seeing no one, and at such distance, which he can’t do. We can’t see no one, but we can look, and not see anyone, which can be said and understood as seeing no one. The play on words works in ancient India, Greece, China, and today in modern English. In Zen Buddhism, Hakuin painted blind men walking carefully on a log bridge several times, as the question had been asked, What does it look like to us that they are blind? What does it look like to see a rat in a maze, and know it can’t see the way out? Do you see it? Do you see and feel it? Do you see and feel and imagine it? You likely don’t talk it out much.
Uddyotakara, a later Nyaya logician, says in his commentary that all sources depend on perception, and sources of knowledge give us a true grasp of things, but there are fake sources of knowledge, and acting on a true source of knowledge leads to success, and acting on a fake source leads to failure. How does failure look, if not like a lack of success, another sort of seeing what you don’t see, or imagined, but did not perceive. The Nyaya Sutra and commentaries tell us that there are problems we can have with the four sources of knowledge, such that we can mis-perceive, and see what isn’t there, or not see what is there, such as unrecognized success or potential talent, even though perception is their primary source, that supports all others insofar as the others are justified.
Perception is seeing or experiencing something for oneself, and can only be valid if it tells you something that doesn’t vary or change. Three examples of false perception given in the sutra are confusing smoke and dust, confusing a rope with a snake, and thinking that the hot earth is wet when in fact this is a mirage. There is a popular modern Indian novel about a man in a loveless arranged marriage who falls in love and has an affair with a prostitute called The Rope and The Snake. Vatsyayana says that some argue that for every thing there is a word and name that is based on conventional practices (vyavahara), and so perceptual thinking is verbal in nature, but this is a mistaken view, seeing words where they aren’t there, as we can look at an object without knowing its name, so perceptual understanding is not dependent on language. (10.11 – 20) His view is remarkably similar to Wittgenstein.
Vatsyayana argues that we can see what we think is smoke and infer there is fire, or hear that there is a fire by testimony, or make comparisons for ourselves from afar, but it is perception, seeing the fire, that is best and that best confirms comparisons, testimony and inferences. Giving a negative example, he similarly argues that seeing a mirage and hoping for water, it is only when we see what isn’t there, the water’s absence, that our inference is disproved. We can also make solid inferences, such as hearing thunder and inferring there was lightning, without making comparisons or hearing the testimony of others.
With knowledge, perception is best. When we learn something from trustworthy testimony, we may still want to know it another way, such as by inference. Understanding by inference, we may still want to know it through experience, but seeing it, the desire to know ceases, as in the example of fire above.
Vatsyayana explains comparison with the example that yak is like a cow, and this is sameness understood in terms of universals, classes of things with shared properties, such as having horns, or having four legs. Comparisons can be valid or invalid, depending on whether or not they are supported by inference, testimony, and of course, perception. Testimony, like perception and the rest, can be valid or not, as we all know from personal experience. Sometimes witnesses lie, and other times they are mistaken, either seeing what they couldn’t have, or not seeing what they could have. There is a psychology experiment that is somewhat well known where a video is shown to subjects of a line at a bank, a shot goes off, and everyone scatters, and some say they see a gun, some say the black guy in line had a gun, and there is no gun, showing racist bias, but also our ability to construct false memories, which can easily become false testimony.
Vatsyayana says inference is the source that comes last, after experience involving perception, analogy and testimony. The Sutra says inference depends on previous perception and is of three types: from something prior, something later, and from something in common. Vatsyayana gives an example of each. If we see swollen storm clouds and infer it will rain, we infer from something prior, inferring an effect from a cause prior to it. If we see an overflowing river and infer it rained up stream, we infer from something later, inferring a cause from the effect later to it. If we infer that the sun was in one place and now another in the sky, we can infer that it moved, as a difference between the two.
The Sutra says (1.1.41) that certainty is grasping something by thinking about possibilities, investigating thesis and counter-thesis, and that the sources can be objects of knowledge themselves, like a measuring scale. Vatsyayana adds that a scale can calibrate a second scale if we weigh gold with the first and then with the second, such that we know the second scale is off or not. Thus, we can use a tried and true knowledge source, like watching with our eyes, to test another knowledge source, like a theory we find in a text or the testimony of witnesses.
The Sutra says that critics (such as Jains and Buddhists, we imagine) could say this leads to an infinite regress, such that no source can be entirely established by other sources. Consider that the first scale could be off, which would mean we can’t use it to check against a second, but where do we know a scale is good without checking it against another? The answer for the Nyaya is that evidence is like the light of a lamp, self-evident in itself, leaning towards positive belief of what seems consistently true as establishing itself as true without controversy. The Nyaya Sutra says sometimes no further source is required, sometimes there is, and there is no fixed rule for determining this. (2.1.20) Because we, like Hindu Nyaya, seek freedom, discipline, pleasure and wealth in this proper descending order of importance, we proceed from what is to what we desire which isn’t.