Nyaya and Vaisheshika are one of the six astika schools of thoughts in Sanatana Dharma (the other four being Yoga, Vedanta, Mimamsa and Samkhya). Both schools, according to me, seem to be having similar views on metaphysics, epistemology, logic, ethics, and soteriology. Then what is the difference between Nyaya and Vaisheshika?
Let me start off by saying that it is natural to ask what the differences are between the Nyaya school and the Vaisheshika school are, because of how closely related they are. First of all, the six Astika schools are often grouped into three groups of two: Samkhya-Yoga, Nyaya-Vaisheshika, and Mimamsa-Vedanta. That's because the Samkhya and Yoga schools both believe in Purusha and Prakriti, they just differ on the existence of a supreme being. Similarly the Purva Mimamsa and Vedanta schools are both focused on analyzing the Vedas, they're just focused on different parts of the Vedas. The Nyaya and Vaisheshika school similarly have much in common: they both believe that the existence of a supreme being can be logically proven, they both believe that the Vedas are authored by that supreme being rather than being authorless, they both believe that the natural elements are eternal rather than arising from either Prakriti or Brahman, etc. They had so much in common, in fact, that eventually they stopped existing as distinct philosophical schools, and merged into a single philosophy, known as Navya Nyaya.
But they do have differences. In this excerpt from his book "Conception of Matter According to Nyaya-Vaisheshika", Umesh Mishra lays out in detail 19 differences between the Nyaya and Vaisheshika. Umesh Mishra's list is summarized in this excerpt from the Encylopedia of Indian Philosophies:
- Nyaya's emphasis on epistemology, Vaisheshika on ontology
- Nyaya has 4 Pramanas, Vaisheshika, 2
- Nyaya has 5 kinds of perception, Vaisheshika only 1
- According to Nyaya inherence is perceptible, but not according to Vaisheshika
- Nyaya is pitharapakavada, Vaisheshika pilupakavada
- Nyaya believes that one motion last 3 or 4 moments, Vaisheshika that it lasts 7 moments.
- Nyaya admits 5 fallacies of the hetu, Vaisheshika, 3
- Nyaya believes that in process there are several vegas produced in turn; Vaisheshika says there is only one
- Nyaya admits sakhandopadis, Vaisheshika includes them under other categories (this applies only to the later schools)
- Vaisheshika admits disjunction produced by disjunction, Nyaya does not
- Vaisheshika holds that 2 and higher numbers are produced by an apekshabuddhi, Nyaya says that the apekshabuddhi only manifests, does not produce those numbers
- Nyaya accepts contact between all-pervading substances,Vaisheshika does not
- The schools differ about the state of the self in liberation
- Nyaya uses the term artha to cover the 5 sense-qualities, while Vaisheshika uses it to cover all substances, qualities, and motions
- Vaisheshika classifies inferences in a fivefold manner (by effect, by cause, by contact, by contradiction, and by inherence), Nyaya thinks this classification useless
- Nyaya says tenderness is separate from hardness and both inhere in contact inhering only in earth, while Vaisheshika says they inhere in touch, not contact
- Naiyayika are Saivas, Vaisheshikas, Pasupatas
- There is reputed to be a difference of viewpoint about organisms, although Mishra thinks there is not
- Nyaya says dreams may be true or false, but Vaisheshika says they are always false.
Whew! Let me just elaborate on the first two differences, since they're among the most important:
Emphasis: The Nyaya school is focused on logical reasoning and argument. In fact the framework of logical argument that the other Astika schools use in their philosophical works and debates comes from the Nyaya school; if you've encountered terms like Pramana, Prameya, Vishaya, Purvapaksha, Siddhanta, Vitandavada, etc., you can see the great debt we owe to the Nyaya school. In short the Nyaya is primarily concerned with epistemology, the study of how we know what is true and what is false. The Vaisheshika school, on the other hand, is focused on ontology, the study of what exists in the Universe. In particular, it subscribes to atomism and contends that atoms are the ultimate cause of the Universe.
In any case, the difference of focus is reflected in what these two schools think is required for Moksha. There isn't much that all the Astika schools agree on apart from the authority of the Vedas, but one of the few things they do agree on is that knowledge of some kind leads to Moksha. What they differ on is what knowledge is required, how to acquire that knowledge, etc. The first Sutra of Gautama's Nyaya Sutras describes the knowledge that the Nyaya school thinks is required for Moksha:
pramāṇa-prameya-saṃśaya-prayojana-dṛṣṭānta-siddhānt-avayava-tarka-nirṇaya-vāda-jalpa-vitaṇḍā-hetvābhāsa-cchala-jāti-nigrahasthānānī tattva-jñānān niśreyasa-adhigamaḥ
It is the knowledge of the real essence (or true character) of the following sixteen categories that leads to the attainment of the Highest Good -
- The means of Right Cognition
- The objects of Right Cognition
- Factors of Inference
- Demonstrated Truth
- Fallacious Reason
- Futile Rejoinders
And the fourth Sutra of Kanada's Vaisheshika Sutras describes the knowledge that the Vaisheshika schools thinks is required:
dharma-viśeṣa-prasūtād dravya-guṇa-karma-sāmānya-viśeṣa-samavāyānāṃ padārthānāṃ sādharmaya-vaidharmyābhyāṃ tattva-jñānān niḥśreyasam
The Supreme Good (results) from the knowledge, produced by a particular dharma, of the essence of the Predicables, Substance, Attribute, Action, Genus, Species, and Combination by means of their resemblances and differences.
The two Sutras end in a similar fashion, but in the case of Nyaya the knowledge required for Moksha has to do with the process of logical argument, whereas in the case of Vaisheshika the knowledge required has to do with the various entities that the Vaisheshika school believes in.
It's also worth noting that the Vedanta school disagrees with both the Nyaya school and the Vaisheshika school; it says that knowledge of Brahman is what's required for Moksha.
Number of Pramanas: The Nyaya school believes that there are four Pramanas or means of valid knowedge: Pratyaksha or perception, Anumana or inference, Sabda or scriptural testimony, and Upamana or comparison. The Vaisheshika school, on the other hand, only believes in two Pramanas: Pratyaksha and Anumana. In that regard it's similar to Buddhism and Jainism. But whereas Buddhism and Jainism reject Sabda Pramana because they reject the Vedas, the Vaisheshika school believes that Sabda Pramana can be reduced to Anumana. They think you can use Anumana to prove that a supreme being exists, then prove that the Vedas were authored by that supreme being, and thereby prove the authority of the Vedas. Here's what the third Sutra of Kanada's Vaisheshika Sutras says:
The authoritativeness of the Veda (arises from its) being the word of God.
By the way, most members of the Vedanta school (apart from Advaitins) believe that there are 3 Pramanas: Pratyaksha, Anumana, and Sabda. That's because Upamana can be reduced to Anumana.