The Nyāya and the Vaiśeṣika are realistic systems based on independent reasoning. They are a valuable set-off against the phenomenalism and idealism of the Buddhist thinkers.
While the Nyāya is mainly logic and epistemology, the Vaiśeṣika is primarily physics and metaphysics. The two, however, agree on essential principles and have the same end, namely, the liberation of the individual self.
As the two systems are closely allied and had been for long treated as parts of one philosophy, they are dealt with here as one.
The history of the Nyāya-Vaiśeṣika extends over twenty centuries. It is divided into two periods, an earlier and a later:
The early Nyāya- Vaiśeṣika begins with Gautama and Kaṇāda (c. 3rd century B.C.) and ends with the advent of Gaṅgeśa (c. A.D. 1200), the founder of the modem School of the Nyāya.
The first systematic work of the Nyāya is the Nyāya-sūtra of Gautama.
Other important works of the early Nyāya are Vātsyāyana's Nyāya-Bhāṣya or commentary on the Nyāya-sūtra (c. A.D. 400), Uddyotakara's Nyāya-vārttika (6th century A.D.),
Vācaspati Miśra's Nyāya-vārttika-tātparya- ṭīkā (9th century A.D.), Udayana's Nyāya-vārttika-tātparya-pariśuddhi (tenth century A.D.) and Nyāya-kusumāñjali (tenth century A.D.), Jayanta's Nyāya-mañjarī and Bhāsarvajña's Nyāya-sāra (10th century A.D.).
Of the Vaiśeṣika philosophy, the first systematic work is the Vaiśeṣika-sūtra of Kaṇāda, which seems to be of an earlier date than the Nyāya-sūtra.
No bhāṣya or commentary on the Vaiśeṣika -sūtra now exists, although we hear of one written by Rāvaṇa, king of Ceylon.
Praśastapāda’s Padārtha-dharma- saṁgraha (4th century A.D.) is generally called the bhāṣya or commentary on the Vaiśeṣika-sūtra. But it is not the character of a bhāṣya and reads like an independent exposition of the Vaiśeṣika philosophy.
On this work of Praśastapāda there are three excellent commentaries, namely, Vyomaśiva’s Vyomavatī 9th century A.D.), Śrīdhara's Nyāya-kandalī and Udayana’s Kiraṇāvalī (10th century A.D.).
Udayana's Lakṣaṇāvalī is a short compendium of the Vaiśeṣika philosophy.
Śivāditya’s Sapta- padārth and Valiabhācārya's Nyāya-līlāvatī are two other important works of the Vaiśeṣika which belong to the end of the early period and anticipate the later Nyāya-Vaiśeṣika philosophy.
The early Nyāya-Vaiśeṣika philosophy may be conveniently divided into two parts, namely, epistemology and metaphysics.
The Nyāya-Vaiśeṣika epistemology deals with all the main problems of knowledge.
Knowledge or cognition, which is an attribute of the self, consists in the manifestation of objects. It is of different kinds.
In the Nyāya it is divided into:
1. prāma or valid and
2. a-prāma or non-valid knowledge.
The first includes: perception, inference, comparison and verbal testimony.
The second includes: memory (smṛiti), doubt (saṁśaya), error (viparyaya) and hypothetical argument (tarka).
In the Vaiśeṣika also knowledge is broadly divided into:
1. vidyā or valid and
2. a-vidyā or non-valid cognition.
But the first includes: perception, inference, memory and intuitive experience (ārṣa-jñāna),
while the second includes: doubt, error, indefinite cognition (anadhyavasāya) and dream (svapna).
True or valid knowledge is a definite or certain(a-sandigdha) and an unerring presentative cognition (anubhava) of the object as it really is.
On this view, doubt, error, hypothetical argument, indefinite cognition and dream are all excluded from pramā or valid knowledge either because they are not certain and definite or not true to the nature of the object.
Memory also is regarded by the Nyāya as a form of non-valid knowledge because it is not a presentative but a representative cognition of some object experienced in the past.
Some Vaiśeṣikas also exclude memory from valid knowledge, although others would regard it as such.
Intuitive knowledge is admitted by the Nyāya as valid, but it is treated as a kind of extraordinary perception.
As to how true knowledge is distinguished from error or false knowledge, the Nyāya-Vaiśeṣika view is this:
Knowledge is true when it agrees with or corresponds to the nature of the object, otherwise it becomes false.
That a knowledge is true is known from the fact that it leads to successful practical activity. If it fails to lead to successful activity it is found to be false.
Thus the truth and falsity of knowledge consist respectively in its correspondence and non-correspondence to the nature of the object known.
And the test of the truth or falsity of knowledge is the success or failure of our practical activities as based on it (pravṛtti-saṁvāda or pravṛtti-visaṁvāda).
This view is known as the doctrine of parataḥ- prāmāṇya and a-prāmāṇya because truth and falsity consist in certain external conditions like correspondence and non-correspondence to facts and are also tested by external conditions like the success and failure of practical activity.
But some Naiyāyikas admit that in certain special cases the truth of knowledge is self-evident (svataḥ-prāmāṇya).
As pramā means true knowledge, a pramāṇa means the unfailing source of such knowledge.
With regard to the number of pramāṇas the Nyāya and the Vaiśeṣika differ:
While the Naiyāyikas generally recognize four distinct pramāṇas, namely:
3. comparison and
4. verbal testimony,
the Vaiśeṣikas recognize onlyperception and inference as separate pramāṇas and reduce comparison and testimony to inference.
Some Naiyāyikas, however, reduce comparison to testimony, while some Vaiśeṣikas recognize memory and verbal testimony also as separate pramāṇas.
Both the Nyāya and the Vaiśeṣika reduce all other pramāṇas like postulation (arthāpatti), non-cognition (anupalabdhi), etc., to one or other of the pramāṇas recognized by them.
Of the pramāṇas,perception(pratyakṣa) comes first and is generally defined in the early Nyāya-Vaiśeṣika as a definite and true cognition of objects produced by sense-object contact (indriyārtha- sannikarṣa).
Another definition of perception which anticipates the modern view is given by some old Naiyāyikas who say that it is immediate knowledge, not due to any previous experience or reasoning.
Perception as a true cognition due to sense-object contact is of different kinds:
It is called external (bāhya) when brought about by the external senses of sight, hearing, touch, taste and smell.
It is internal(āntara, mānasa) when due to the contact of the mind, the internal sense, with its proper objects.
Perception is also divided into the two kinds:
1. of nir-vikalpaka or indeterminate and
2. sa-vikalpaka or determinate.
Indeterminate perception is the cognition of an object as just an existent thing without any explicit recognition or characterization of it as this or that kind of thing.
It is an apprehension of the existence and qualities of an object without any verbal judgment of it as a subject of which the qualities are predicated.
Determinate perception is the cognition of an object as possessed of some character, or as the subject of certain qualities which are predicated of it.
Pratyabhijñā or recognition is regarded by the Nyāya-Vaiśeṣika as a kind of sa-vikalpaka perception. It is the cognition of an object as what was cognized before and, therefore, qualified by past experience as when one says:
“This is the same jar that I saw.”
After perception comes anumāna or inference.
It is a process of reasoning in which we know some unperceived character of a thing through the medium of a mark which is found present in the thing and is known to be universally related to that character:
Thus we infer the existence of unperceived fire in a hill when we observe smoke in it and remember that smoke is always related to fire.
The hill with regard to which we infer fire is called the pakṣa or subject of inference. The fire which we infer in relation to the hill is called the sādhya or object of inference.
And the smoke which serves as the mark or sign of the unperceived fire in the hill is called the linga, hetu or reason.
But the smoke is the mark of fire in the hill because it is perceived to be present in the hill and known from previous experience to be invariably related to fire. The presence of the mark, linga, in the pakṣa, hill, is technically called pakṣa-dharmatā, and
the relation of invariable and unconditional concomitance between the linga, smoke and the sādhya, fire is called a-vinā-bhāva or vyāpti.
The ground of inference is, therefore, not the linga as such, but a consideration of it as invariably related to the sādhya and present in the pakṣa. This consideration is called linga-parāmarśa.
It would appear from the above that an inference must contain three terms and at least three propositions:
The three terms of an inference are pakṣa, sādhya and linga which correspond respectively to the minor, major and middle terms of the syllogism in Aristotelian Logic.
The process of inference consists in relating the sādhya or major term to the pakṣa or minor term through the relation of the linga or middle term to the pakṣa or minor term, on the one hand, and the sādhya or major term on the other.
This gives us three propositions, of which:
the first is a predication of the sādhya with regard to the pakṣa, e.g. “The hill is fiery.”
The second is the affirmation of the linga as related to the pakṣa, e.g. “Because the hill is smoky.”
The third is the affirmation of the lingaas universally related to the sādhya, e.g. “All smoky objects are fiery, as the kitchen.”
This gives us a three-membered syllogism which is used when one infers something for himself.
But an inference which is meant to prove or demonstrate a truth has five avayavas or members. The 5 members and their order are as follows:
1. Pratijñā or an assertion: The hill is fiery.
2.Hetu or the reason: Because it is smoky.
3.Udāharaṇa or the general proposition with examples: All smoky objects are fiery, e.g. a kitchen.
4.Upanaya or the application: So is the hill smoky.
5. Nigamana or the conclusion: Therefore the hill is fiery.
Here then we have a syllogism consisting of five categorical propositions.
There are certain points-of similarity between the Indian and the Aristotelian syllogism. In both there are only three terms.
The three-membered syllogism has three propositions which correspond to the conclusion, the minor and the major premise of Aristotle’s syllogism.
In view of such similarity some scholars think that the development of the Indian syllogism is due to the influence of Aristotle. But there are certain fundamental differences between the two which make it difficult to accept this view:
Even in the three-membered syllogism the order of the propositions in Aristotle’s syllogism is reversed.
The fundamental rule of Aristotle's syllogism, the dictum de omni et nullo, rests solely on the relation of class inclusion, whereas the main principle of the Indian syllogism is the relation of invariable and unconditional concomitance between the middle and the major term.
Further, Aristotle's syllogism is purely formal and guarantees only the formal validity of the conclusion. It is more like an implication than an inference.
If we assert the truth of its premises that of the conclusion can be asserted. The Indian syllogism is a real inference in which from premises asserted as true we come to a true and necessary conclusion.
The third premise of the Indian syllogism is a general proposition based on particular facts of experience. It thus combines deduction with induction, formal validity with material truth.
The fourth premise of the Indian syllogism makes a synthesis of the major and the minor premises to bring out the identity of the middle term in them. That such a synthesis is a necessary step in syllogistic inference is admitted by some modern Western logicians.
There is no part of the Aristotelian syllogism which corresponds to the fourth proposition of the Indian syllogism.
The Nyāya-Vaiśeṣikas give different classifications of inference. The distinction betweensvārtha and parārtha anumāna, i.e. inference for oneself and inference for convincing other people, is common to both.
The three kinds of pūrvavat, śeṣavat and sāmānyato-dṛṣṭa inference given in the Nyāya are replaced by the two kinds of dṛṣṭa and sāmānyato-dṛṣṭa in the Vaiśeṣika.
An inference is pūrvavat or śeṣavat according as it passes from a perceived cause to an unperceived effect, or from a perceived effect to an unperceived cause.
It is called dṛṣṭa when based on a previously observed invariable relation between the middle and major terms.
It is sāmānyato-dṛṣṭa when based on an invariable relation observed between objects which are similar to the middle and the major, as when one infers the existence of sense-organs from cognitive functions on the ground that an action like cutting requires an instrument, say, an axe.
Again, inference is said to be of three kinds, i.e. kevalānvayin, kevala-vyatirekin and anvaya- vyatirekin.
It is kevalānvayin when based on a middle term which is always positively related to the major, kevala-vyatirekin when the middle is only negatively related to the major and anvaya-vyatirekin when the middle is both positively and negatively related to the major term.
There are five kinds of fallacies of inference (hetvābhāsa) generally recognized by the Nyāya-Vaiśeṣikas, although some of them give their number as three or four or six.
These are all fallacies of the hetu or the middle term and are called (1) sa-vyabhicāra, (2) viruddha, (3) sat-pratipakṣa, (4) a-siddha, (5) bādhita.
The sa-vyabhicāra or the irregular middle is not uniformly concomitant with the major term, but is sometimes present even where the major is absent, as when “fire” is taken as the middle term of an inference to prove the existence of “smoke.”
The viruddha or the contradictory middle is that which proved the contradictory of what it is intended to prove. This is illustrated when one argues: “Sound is eternal, because it is caused,” for what is caused is non-eternal.
The sat-pratipakṣa is the inferentially contradicted middle. It is the middle term of an inference, of which the conclusion is validly contradicted by another inference. The inference: “Sound is eternal, because it is audible,” is validly contradicted by another inference: “Sound is non-eternal, because it is produced.”
The a-siddha or sādhya-sama is a middle term which is not a real fact, but an undue assumption, as when one argues: “The sky- lotus is fragrant, because it has lotusness in it like a natural lotus.”
The bādhita is a middle term, the non-existence of whose major is ascertained by means of some otherpramāṇa. This is illustrated thus: “Fire is cold, because it is a substance.” Here the coldness of fire is disproved by perception.
These five kinds of material fallacies have each many subdivisions. Other fallacies like chala, jāti and nigraha-sthāna which arise out of equivocation, ambiguity, misunderstanding, etc., are separately treated by the Nyāya.
This classification is like the Aristotelian classification of fallacies into those in dictione and those extra dictionem, in which also the formal fallacies of inference like undistributed middle, illicit process and so on are not included.
Upamāna or comparison is the third source of knowledge recognized by the Nyāya.
It gives us the knowledge of the relation between a name and things so named on the basis of a given description of them in terms of their similarity or dissimilarity to certain familiar objects.
A citizen who does not know what a “gavaya” or wild cow is, may be told by a forester that it is just like the familiar cow. If subsequently he happens to meet with such an animal in the forest and recognizes it as a gavaya, then his knowledge will be due to upamāna.
The Nyāya view of upamāna is different from that of the Mimāṅsā and the Vedanta.
Śabda or testimony is the last pramāṇa admitted by the Nyāya. It consists in the statement of a reliable person about things of which he has a direct knowledge.
Those who have no direct experience of such things may have a true knowledge of them from the statement of the reliable person.
Such knowledge being due neither to perception nor to inference, testimony is admitted as a distinct source of knowledge in the Nyāya and many other systems of Indian philosophy.
There are two kinds of śabda, namely, that relating to perceptible objects (dṛṣṭārtha) and that relating to imperceptible objects (a-dṛṣṭārtha):
The first includes the testimony of reliable men and the Scriptures bearing on perceptible objects of this world.
The second includes both human and Scriptural testimony bearing on supersensible realities like soul, God, immortality, etc.