Nyaaya literally means, "that by which the mind is led to a conclusion". The grammarian Paanini derives the word Nyaaya from the root 'i' which conveys the same meaning as 'gam' so it is etymologically identical with 'nigama' or the conclusion of a syllogism.

HISTORICAL DEVELOPMENT

Initially this system of philosophy relied heavily on reasoning. However it evolved to give due authority to the Vedas.In many of the Puraanas we find attacks on logicians.

Faced with the skepticism of the Buddhists who had dislodged traditional beliefs regarding the world, God and Self, the Nyaaya strives to restore the traditional substances, God, the Self within and the world without. But this could not be done by merely appealing to scriptural authority, because the heterodox sects had based their claims on the base of reason.So, the Nyaaya attempts to combat heretical views regarding knowledge of the world on the basis of pure logic and reason. The school advocates a philosophy of atomism, spiritualism, theism, realism and pluralism. While its sister system - the Vaishesika provides a metaphysical and ontological classification of the world, the Nyaaya concentrates on logic and epistemology - especially with regards to Pramaana or the means of right knowledge.

The system is also called Taarkashaastram or the science of reasoning, Pramaanashaastram or the science of epistemology, hetuvidya or the science of causes, vaadavidya or the science of debate, tattva shastra or science of categories and Anvikshiki or the science of critical study.It is also called, phakkika shastra or science of sophistry. The Sarvaadarsana Sangraha mentions Nyaaya as the Akshapaada system.

LITERATURE

The sage Gautama or Gotama (5th century BC) also known as Akshapaada or Medhatithi or dirghatapas who wrote the Nyaaya Sutra is considered the founder of the school.

The Vaayupurana mentions akshapada as a disciple of Soma Sharma. This akshapada mentioned alongside with Kanaada seems to refer to Gautama. As to the origin of the name Akshapaada, legend has it that Gautama was so deeply absorbed in philosophical contemplation that he fell into a well and God provided him with a second pair of eyes in his feet.

Vatsyaayana's (4th century CE) Nyaaya Bhaashyam is the celebrated commentary on the Nyaaya Sutra. Udhyotakaara (6th century CE) has written Nyaaya Vaartikam. Vacaspati Mishra's works on the Nyaaya are Nyaayavaartikataatparyatika, Nyaayasuchinibandha and Nyaayasutrodhara.

Udhayaana's (9th century CE) is a famous logician of this school whose works are Tatparyaparishuddhi, Atmatattvaviveka, Kusumaanjali, Kiranaavali and Nyaayaparishista. An independent commentary on the Nyaaya Sutra is Jayantha's Nyaayamanjari.

A survey of the school's doctrines is found in Bhaasarvajna's Nyaayasara (10th century CE). A commentary on Udhayaana's Nyaayataatparyaparishuddhi is Vardhamaana's Nyaayanibandhaprakaasha (1225 CE). Vardhamaana's views are developed by Rucidatta in his Makaranda (1275 CE). Varadharaaja's Tarkikaraksha (12th century CE). Keshava Mishra's Tarkabhaasa (13th century CE) openly combine Vaishesika views with the Nyaaya. Other works include Vardamanendu by Padmanabha Mishra, Nyaayalankaara by Srikantha, Nyaayalankaara vritti and Nyaayamanjari by Jayanta.

Navya Nyaaya is the modern school of Nyaaya where the logical aspect of the original school is given more attention. The standard text of this school is Gangesha's Tattvachintaamani (12th century CE). Jayadeva's Aloka (13th century CE) is a commentary on Gangesha's work. Vasudeva Sarvabhauma's Tattvachintaamanivyaakya (15th century CE) is considered the first great work on the Navadvipa school. Jagadeesha and Gadaadhara (15th and 16th century CE) are well known logicians of this school. Annam Bhatta (17th century CE), a telugu brahmin, combines the views of the ancient Nyaaya and Vaishesika with the modern Nyaaya in his Tarkasamgraha and Deepika. Vallabha's Nyaayaleelaavati and Vishvanaatha's Nyaayasutravritti are other works of some importance.

NATURE OF KNOWLEDGE

According to the Nyaaya Sutra, Misapprehension, faults, activity, birth and pain these constitute the world. It is due to misapprehensions that attachment or aversion develops towards objects. From this attachment or aversion springs the faults - envy, jealousy, deceit, avarice etc. Influenced by these a man commits misdeeds, which results in the accumulation of karma and hence transmigration. This causes pain.

By a true knowledge of the 16 categories misapprehensions are removed and faults disappear.Then the person is no longer subject to activity and freed from transmigration and pain.

Right knowledge is the knowledge about the true nature of the sixteen categories - means of right knowledge (pramaana), object of right knowledge (prameya), doubt (samsaya), purpose (prayojana), familiar instance (drishtaanta), established tenet (siddhaanta), members of a syllogism (avyava), confutation (tarka), ascertainment (nirnaya), discussion (vaada), wrangling (jalpa), cavil (vitanda), fallacy (hetvaabhaasa), quibble (chhala), futility (jaati) and occasion for rebuke (nigrahastaana).

Being realists, the Naiyaayikas accept the distinct identity of known, the knower and knowledge - for perception to arise there must be an object distinct from the percipient. As a lamp illuminates objects placed before it, knowledge too reveals objects, which come before it. But this knowledge itself can be valid or invalid. That which leads to the right apprehension of the object and corresponds with reality is valid knowledge.

When the Self comes into contact with the non-self, knowledge arises. Knowledge is an adventitious property of the Self. If the conditions, which give rise to knowledge are sound, knowledge too is sound. If the conditions are defective, likewise the knowledge obtained. A man with healthy vision sees a conch white, but a man with jaundice sees it yellow. Valid knowledge corresponds to the object and leads to successful activity. Invalid knowledge doesn't correspond with the objects and leads to failure and disappointment. But knowledge is only the manifestation of the object, while its validity is something, which is subsequent to already arisen knowledge.

MEANS OF KNOWLEDGE

1. Pramaana

The four means of valid knowledge are pratyaksha or perception, anumaana or inference, upamaana or comparison and shabda or verbal testimony. Invalid knowledge includes memory (smrithi), doubt (samshaya), error (viparyaya) and hypothetical reasoning (tarka).

1.1 Pratyaksha or perception
The Nyaaya Sutra defines pratyaksha or perception as : "non-erroneous cognition which is produced by the contact of the sense organs with the objects, which is not associated with a name and is well defined". Unlike inference, comparison or verbal testimony, pratyaksha is not knowledge acting on already existent knowledge. It is the direct and immediate cognition of the object without any interference from any other form of cognition. The senses perceive, the mind receives and passes the knowledge to the Self. The mind is the mediator between the senses and the Self and being atomic it can handle only one perception at any point in time. The contact between the object and the senses, presupposes the contact between the senses and the mind and between the mind and the Self.

Perception itself happens in two stages - nirvikalpa or indeterminate perception and savikalpa or determinate perception. When an object is first perceived, only its bare features are apprehended and there's no identification at that moment - this is indeterminate perception. It's only later that memory and reason kick in and the identification is made - this is determinate perception. While the first stage is bare sensation devoid of differentiation, relationship, assimilation, discrimination, analysis and synthesis, the second stage is conceptual knowledge involving assimilation, relationship and synthesis. Indeterminate knowledge is bare sensing, while determinate knowledge is knowing and identifying. But this kind of a distinction itself is only conceptual and cannot be made in reality.

Perception is of two kinds - ordinary or laukika and extraordinary or alaukika.
Ordinary perception itself is divided into internal (maanasa) and external (baahya). Internal perception is effected when the mind comes into contact with psychical states and processes like pain, pleasure, affection, desire, aversion etc. External perception takes place when the sense organs come into contact with external objects. The five sense organs of sight, sound, touch, taste and smell have their respective perceptions in visual, auditory, tactual, gustatory and olfactory. Earth, water, fire, air and ether make up the five external sense organs and thus each sense organ senses the particular quality of its element. The atoms of the earth make up the sense organ of smell - the nose. So the nose perceives smell, which is the specific quality of earth.

Extraordinary perception is of three kinds - saamaanyalakshana or the perception of universals, jnaanalakshana or the perception through memory and yogaja or the intuitive yogic perception. As with Vaishesika, the universal is considered as a distinctly real entity by the Nyaaya. An individual belongs to a particular class because the universal of the class inheres in it - so a cow is a cow because of the universal cowness inhering in it. Since usually only the particulars are perceived and not the universal ie only a cow and not a universal cow is perceived - the Nyaaya thinks that the universal is perceived extraordinarily. In Jnaanalakshana, different sensations though memory become associated and form one integrated perception. When we see a garbage dump at a distance, we immediately say ,"there's a smelly dump". Here even though we have only visual perception of the object, through memory we associate the related smell due to past cognition and thus an integrated perception results. Yogaja perception is the intuitive yogic perception of all objects past, present and future. It is a supra sensuous and supra relational insight similar to the Kevalajnaana of the Jainaas or the Bodhi of the Buddhists or the Aparokshaanubhuti of the Vedantins.

1.2 Inference or anumaana
Inference is that cognition which presupposes some other cognition. It is knowledge, which arises based on previous knowledge. There can be no inference in the absence of perception. When we see smoke on the hill, we infer that the hill is on fire. Here the hill is the minor term (saadhya), the smoke the middle term (paksha) and the fire the major term (linga or hetu). We know that smoke is invariably connected with fire - this is the invariable concomitance (vyaapti), which is the nerve of inference. Thus inference is the knowledge of the presence of the major in the minor through the middle, which resides in the minor and is invariably associated with the major.

Inference is from a particular to a particular through the universal.
Inference is of three kinds - purvavat, sheshavat and saamaanyatodrashta. When we infer an unperceived effect from a perceived cause we have purvavat inference e.g, like when we infer impending rain from dark clouds. Sheshavat inference is when we infer an unperceived cause from a perceived effect e.g., like when we infer past rain from floods. Samaanyatodrashta is inference based on the uniformity of coexistence e.g., like when we infer cloven hoofs of an animal by its horns.

Inference is also classified as kevalaanvayi, kevalavyatireki and anvayavyatireki. This classification is based on the different methods to establish universal concomitance.

In the first case - kevalaanvayi - the middle term is always positively related to the major term :

Only things with wings can fly.
The dove has wings.
The dove can fly.


In kevalavyatireki, the middle term is always negatively related to the major term :

When there're stars in the sky, it will not rain.
Today there are stars in the sky.
Today it will not rain.


Anvayavyatireki inference is when the middle term is both positively and negatively related to the major term :

All things, which have smoke have fire. No non-fiery things have smoke. The hill has smoke and is not non-fiery. The hill is on fire.

1.3 Upamaana or Comparison
It is knowledge of resemblance or similarity and corresponds roughly with analogy. Suppose a man has never seen a tiger and a cat is pointed out to him and he's told that a tiger is the massive version of a cat, yellow in color with black stripes. So when he sees a tiger in the forest, his recognition/knowledge of it as a "tiger" is due to upamaana or comparison. Upamaana is the knowledge of the relation between a word and the object it signifies.

1.4 Shabda or Verbal Testimony
Shabda is of two kinds : vaidika and laukika. The former is the scripture, the Veda, which is perfect and infallible as they are the utterances of God. Laukika or secular testimony being the utterances of humans is liable to error. Only the words of wise trustworthy men (Aptavaakya) who are always known to speak the truth are valid. A word has the power to convey the meaning of the object it signifies. A collection of words make a sentence. Sentences to be intelligible must conform to certain standards :

1. Akaankshaa - the words should be in a proper order to convey the correct meaning.
2. Yogyataa - the words should posses the fitness to convey the sense and should not contradict the meaning e.g., water the plants with fire.
3. Sannidhi - the words should be spoken in quick succession. If there's too much of a pause or intervals between words, there'll be no logic to the sentence.
4. Taatparya - the intention of the speaker when ambiguous words are used. When one is eating and asks for 'saindhava', which means both salt and horse, he should not be brought a horse.

Invalid knowledge as noted before includes memory, doubt, error and hypothetical reasoning. Memory is invalid as it is representative rather than presentative i.e., the object is not directly apprehended by the Self, but indirectly recalled based on past experience. Uncertainty in cognition is doubt and misapprehension is error. An example of hypothetical reasoning is, "if there were no sun, there cannot be light" - it is not real knowledge as it starts with a wrong assumption to show how it can lead to absurdities.

2. Object of right knowledge (prameya)

Soul, body, senses, Objects of sense, intellect, mind, activity, fault, transmigration, fruit, pain and release are the objects of right knowledge.

3. Doubt (samsaya)

Doubt is a conflicting judgement about the precise character of an object. It is of five kinds depending on what it arises from:

1. Recognition of several common properties:
   e.g. seeing a tall object in twilight we cannot decide if it is a post or a person ie tallness is a common property.
2. Recognition of uncommon properties :
   e.g. on hearing a sound one questions if it is eternal for the property of sound does not abide in non-eternal things nor in eternal things
3. Conflicting testimony
   One cannot affirm the existence of soul by mere study of different philosophies as each state a conflicting view
4. Irregularity of perception
   e.g. a mirage
5. Irregularity of non-perception
   perception of water in radish (where it exists) or in dry-land(where it does not)

4. Purpose (prayojana)

Purpose is that which one endeavors to avoid or attain.

1. Familiar instance (drishtaanta)
   This is a thing about which a laukika and an expert have the same opinion eg where there is smoke there is fire.
2. Established tenet (siddhaanta)
   An established tenet is a dogma resting on the authority of a certain school etc. This is of four kinds :
   dogma of all schools eg 5 elements,
   dogma peculiar to one school eg eternity of sound is peculiar to mimamsakas
   hypothetical dogma and
   An implied dogma.
   
3. Members of a syllogism or Avayava :
   There are five members in the Nyaaya syllogism :
   
   1. Pratijnaa or proposition - the hill is on fire.
   2. Hetu or reason - because the hill has smoke.
   3. Udhaarana or example - whatever has smoke has fire e.g., an oven.
   4. Upanaya or application of the universal concomitance to the present case - the hill has smoke, which is invariably associated with fire.
   5. Nigamana or conclusion drawn from the preceding propositions - therefore the hill is on fire.

4. Confutation (tarka)
   Confutation is carried on for ascertaining the true nature of a thing which is not known is the reasoning by which the conclusion otherwise is shown as being absurd.
5. Ascertainment (nirnaya)
   This is the removal of doubt and determination of the object by hearing both the paksha and praipaksha ie the opposing views
6. Discussion (vaada)
   This is the adoption of one of the two opposing sides, and analysed by the avayavas, defended by the Pramaanas, facing the opponent with tarka.
7. Wrangling (jalpa)
   Wrangling aims only at gaining victory and is done by cavil, fallacy, quibble and futility and all those which deserve rebuke.
8. Cavil (vitanda)
   This consists of mere attacks on the opposite side.
9. Fallacy (hetvaabhaasa) :
   Five kinds of fallacies (hetvaabhaasa) related to the middle term are recognized in the construction of an inference :
   1. Asiddha or Sadhyasama : If the middle term is not present in the minor term then we have the fallacy of the unproved middle term. This fallacy itself can be divided into three.
      1. Ashrayasiddha - if the minor term itself is unreal, what's the validity of the middle term? E.g., the sky-lotus is a flower; all flowers are fragrant; the sky-lotus is fragrant.
      2. Svarupaasiddha - here the middle term by its very nature cannot be present in the minor term. E.g., silk is like gravel; gravel is rough; silk is rough.
      3. Vyaapyatvaasiddha - here the universal concomitance (vyaapti) between the middle and the major term is conditional. E.g., fire smokes only with wet fuel. A red hot iron ball doesn't smoke. So the statement, "wherever there's fire, there's smoke", is wrong. As the middle term is conditioned, it's fallacious to say ,"the hill has smoke, because it has fire".

   2. Savyabhichaara or Anaikaantika : This is the fallacy of the irregular middle and is of three kinds :
      1. Sadhaarana - Here the scope of the middle term is too wide e.g., the hill is on fire, because it has trees. There may be a lot of hills with trees, which are not on fire.
      2. Asaadhaarana - Here the scope of the middle term is too narrow e.g., sound is eternal, because it is audible. Here audibility belongs to sound only and is not present anywhere else.
      3. Anupasamhaari - Here the middle term is non-exclusive and the minor term is all inclusive e.g., all things are non-eternal, because they are knowable.

   3. Satpratipaksha : Here the middle is contradicted by another equally valid middle e.g., the Self is the reality because it is what gives ultimate meaning to our existence; the Self is not the reality because the feeling of "selfness"/ego is the greatest obstacle to realization.
   4. Baadhita : Here the middle is contradicted by some other valid source of knowledge e.g., fire is cold because it is a substance. Since perception proves that fire cannot be cold, the middle term, "substance" is contradicted.
   5. Viruddha : Here instead of proving the major terms presence in the minor term, the middle actually proves its non-existence e.g., sound is eternal, because it is produced. Anything which is produced has to cease ie it is temporary and thus sound cannot be eternal.

10. Quibble (chhala)
    Quibble is an opposition by assumption of an alternate meaning. This may be by taking a term in a sense other than that the speaker intended to, in respect of a genus or in respect of a metaphor
    e.g1. A person says This boy is a nava kambala meaning having a new blanket.
    Opposing this saying that he is not since he does not have nine blankets ie taking the word nava as nine instead of as new.
11. Futility (jaati)
    This consists of offering objections founded on mere similarity or dissimilarity.
12. Occasion for rebuke (nigrahastaana).
    This arises on wrong deduction or when one does not understand at all.

METAPHYSICS

The metaphysics of the Nyaaya is quite similar to that of the Vaishesika. God, Selves and atoms make up the world. The atoms are co-eternal with the infinite Selves and both are beyond creation and destruction. Atoms are set into motion to combine (production) to form objects or dissolved (destruction) by the unseen power (adhrshta), which is guided by God. Thus God using the unseen power is the efficient cause of the world. The object born out of the combination of atoms is a totally new thing and has distinctive features of its own

CAUSALITY

According to the Nyaaya a cause is the invariable and unconditional antecedent of the effect and an effect is the invariable and unconditional consequent of the cause. The same cause produces the same effect and the same effect is produced by the same cause. Plurality of causes is ruled out. The three characteristics of a cause is :

1. antecedence -the cause must precede the effect (purvavritti),
2. invariability - the cause must invariably precede the effect (niyatapurvavritti) and
3. unconditionality - the cause must unconditionally precede the effect (ananyathaasiddha).

Five kinds of accidental (anyathaasiddha) antecedents, that are not real causes, are recognized by the Nyaaya

1. The qualities of a cause are only accidental antecedents - the color of a potter's staff is not the cause of the pot produced.
2. The cause of the cause or a remote cause is not unconditional - the father of the potter is not the cause of the pot.
3. The co-effects of a cause are not causally related - the sound produced by the potter staff, though it may invariably precede the pot produced, is not the cause of a pot.
4. Eternal substances like space are not invariable antecedents.
5. Unrelated things like the potter's donkey though invariably present at the time of the production of the pot, is not the cause of the pot.

A cause is an unconditional and necessary antecedent of the effect. The same effect is produced by the same cause and never another. Cause and effect are sequential and are never simultaneous.

Contrary to the Samkhya position which advocates the prior existence of the effect in the cause (satkaaryavaada), the Nyaaya like the Vaishesika advocates the opposite - (asatkaaryavaada) - that the effect is a totally distinct from the cause, a fresh creation. It was non-existent before its creation and is newly brought into existence by the operation of the cause.

There are three kinds of causes :

1. samavaayi or the material cause - the cloth cannot exist apart from the threads which constitute it or the pot exist apart from the clay of which it is made. The effect inheres in its cause.
2. asamavaayi or non-inherent cause - It is that which inheres in the material cause and helps in the production of the effect. The color of the thread is the non-inherent cause of the color of the cloth.
3. nimitta or the efficient cause - the weaver who produces the cloth, the loom or those accessories used in the production of the effect is the efficient cause of the cloth produced.

THE SOUL AND ITS LIBERATION

The Nyaaya uses inference to prove the existence of the Self and considers it the object of the notion "I". The synthesis of varied cognition and the apprehension of these by a single knower proves the existence of the Self. The eternal, indivisible and all pervading Self is the knower, enjoyer and doer. It is distinct from the senses, body and mind. The individual Self is the substratum of the quality of consciousness, which is not its essence but an accidental property. By itself it is just an unconscious (jada) principle and consciousness is due to its conjunction with the mind during the waking state. Due to ignorance and karma it falls into bondage. Connected with its manas (mind) during its empirical life it experiences the world. Right knowledge and destruction of karma liberates the Self and it is separated from the manas.

Right knowledge is not obtained from mere books. Scriptural study, philosophical thought, practice of virtue, reflection, yogic practices and meditation enables one to discriminate between the Self and the non-Self.

Moksha is supreme facility marked by perfect tranquility and freedom from defilement. It is not a state of pleasure but only the cessation of pain. It is the complete cessation of effort, activity, consciousness and absolute cessation of the Self from the body and mind. Devoid of knowledge or joy, it is a state similar to deep dreamless sleep.

GOD

The Nyaaya is openly theistic. Drawing its followers from the Saiva and the Paashupatha sects, this school more than any other orthodox school prior to the rise of the bhakti schools of Vedanta, championed the cause of theism defending it against the attacks of heretical schools - especially the Buddhists. God is the supreme Self who possesses all the six perfections in their fullness - majesty, power, glory, beauty, knowledge and freedom. He is the moral governor of all beings (prayoja kartaa) and is both omnipotent and omniscient. In his Kusumaanjali, Udhayaanaachaarya gives nine arguments as proof of the existence of God :

1. An intelligent cause is needed to explain the order and design of the world. God is the efficient cause who is the coordinating principle between different phenomena.
2. A guiding principle is needed to activate the unseen power (adhrshta) to set the atoms in motion for the creation of the world.
3. The unseen power is unintelligent and to create, sustain and destroy requires God's will.
4. A word has a meaning and signifies an object. The power of the word to signify an object comes from God.
5. The scripture (Veda) is authored by God.
6. The Veda is the proof for the existence of God.
7. It is God who through the injunctions and prohibitions in the Veda, has set the moral law.
8. The magnitude of the dyad is produced by the number of two atoms, which constitute it. While number one is directly perceived, the other numbers are conceptual creations. At the time of creation everything - atoms, adhrsta, the Selves, space, time and minds - are all unconscious. So the numerical conception needed at the time of creation is only due to the divine consciousness.
9. The stock of merit and demerit which accrue from our actions is adhrshta or the unseen power. But being unintelligent, adhrshta requires the power of God.

Though the metaphysics of the Nyaaya attracted a lot of criticism from rival schools, the standards it set in epistemology and logic, has been accepted by most schools of Indian philosophy. The student of Indian philosophy can hardly underestimate the value of Nyaaya in the study of the subject.

In fact, of the 6 ancient schools of Hindu philosophy, only 2 are said to have living followers and an unbroken tradition- Nyaaya, and Vedanta.