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In view of the importance of Prasaṅgānumāna as a logical weapon used with telling effect in the philosophical literature of medieval India and in view of the divergence of opinion regarding its validity as an instrument of knowledge, we propose to give an exposition of the nature and function of prasaṅgānumāna. It is a hypothetical negative argument devised to point out logical defects in the position of the adversary. The wordprasanga’ has been given as the synonym of ‘tarka’ by Vācaspati Miśra and ‘tarka’ though included in the list of the sixteen logical categories enunciated in the first aphorism of the Nyāyasūtra, is not regard-ed as an- independent instrument of valid knowledge by the Naiyāyikas. It is regarded as an indirect proof,.requisitioned to strengthen the desired conclusion by showing that the contradictory is not a supposable alternative.

Tarka has been defined by Jayanta as

“Presumptive evidence in favour of one of the two doubtful alternatives by showing the reason conducive to the establishment of the thesis.”[1]

“In tarka, or indirect proof, we start with a wrong assumption and show how it leads to absurdities............ The admission of a false minor necessitates the admission of a false major.”[2]

“The older Nyāya admits eleven kinds of tarka which the modern reduce to five, of which the chief is the reductio ad absurdum, called pramāṇa-bādhitārtha-prasaṅga. The other four are ātmāśraya, or ignoratio elenchi (?); anyonyāśraya, or mutual dependence; cakraka, or circular reasoning, and anavasthā, or infinite regress. Even the reductio ad absurdum is regarded as a case of fallacious reasoning, since it derives a conclusion which is absurd.”

Prasaṅgasādhana can be subsumed under the last variety of tarka, viz., the ‘reductio ad absurdum,’ subject to a necessary qualification. Prasaṅgasādhana differs in a very material respect from ‘ reductio ad absurdum,’ viz., that whereas the latter is requisitioned to prove the justice or correctness of a particular syllogistic argument by showing the contradictory supposition to be false, the former is employed for exactly the opposite purpose. According to modern Nyāyareductio ad absurdum’ has a twofold utility; first, it serves to establish the universal proposition, the major premise, in which- the invariable concomitance of the middle term with the major term is enunciated (vyāptigrāhaka); secondly, it serves to- prove the correctness of the conclusion established (viṣayapariśodhaka). The last variety corresponds to the ‘reductio ad absurdum’ of European logic, which “consists in showing that the supposition of the contradictory of the given conclusion is false and so, by opposition, the given argument is correct.” The logical procedure is the same, viz., showing the absurdity of tbe contradictory supposition. The logical principle and procedure are also the same in the case of prasaṅgānumāna and tarka; the difference lies in the application. The former is employed for demonstrating the falsity of a given argument—thereby showing the logical necessity of the contradictory position being accepted; In fact, prasaṅgasādhana can be included under ‘pratibandhī,’ a variety of tarka enunciated by older Naiyāyikas The ordinary rule of debate requires that the middle term must be acceptable to both the parties (ubhayasiddha) and that the probandum (sādhya) must be a fact. But the requisite conditions of prasaṅgānumāna are that (1) the probans (hetu) is false and assumed for argument’s sake on the statement, of the opponent and is not accepted as true by the arguer (vādin) himself, and (2) consequently the probandum is a false issue, which is forced upon the adversary; (3) the main implication of such argument is of course the truth of the contradictory position, which decisively invalidates the assumption of the adversary. This form of argument has been very frequently employed with advantage by Buddhist philosophers against their adversaries. It is, however, significant that Dharmakīrti in his Nyāyabindu is very emphatic on the point that the probans must be approved by both the parties in a debate. He has, therefore, included in his catalogue of fallacious reasons those middle terms which are not accepted by either of the parties (vādin or prativādin). It is plain, therefore, that prasaṅga-hetu (a falsely assumed middle term) has no place in the scheme of Dharmakīrti’s logic, and probably also in Dignāga’s system,[3] which has been mainly followed by Dharmakīrti. In the Nyāyapraveśa and the Hetutattvopadeśa of Jitāri also,[4] a middle term, which is not approved by common consent, has been declared to be a fallacious reason.

Although the attitude of the orthodox Buddhist logicians is not friendly to such forms of argument, it is not undeniable that it has played a very prominent part in the evolution of philosophical thought in India. Candrakīrti, in the course of his comments on the first verse of the Mādhyamika Kārikā of Nāgārjuna, has taken elaborate pains to elucidate the Mādhyamika’s position in logic. Notwithstanding the fact that the metaphysical position of absolute scepticism, which he adopts, precludes him from admitting the truth of, and so advancing at his own initiative, any of the premises of a syllogistic argument, the Mādhyamika can, Candrakīrti argues, refute the arguments of his antagonists without prejudice to his philosophical predilections by the aid of Prasaṅgānumāna. He, however, declines to be committed to the necessity of the contradictory proposition being established, as a Mādhyamika cannot have ex hypothesi any position of his own. He thinks that his duty consists in showing contradiction in the adversary’s position and not in proving any particular thesis of his own. in fact, he has no thesis in philosophy save and except that nothing can be proved.[5] A divergence of opinion regarding the necessity of the contradictory position being accepted, which is the third condition of prasaṅgānumāna, seems to have been responsible for the two main divisions of Nāgārjuna’s followers into the Prāsaṅgika and Svātantrika schools, the latter insisting on the necessity of independent arguments for the refutation of the Contradictory implication of a prasaṅgānumāna. So in this respect the historical importance of prasaṅgānumāna cannot be over-estimated. Śrīdhara in his Nyāyakandalī makes mention of prasaṅgasādhana which is the same thing as prasaṅgānumāna, sādhana and a numāna being synonymously used.

He says

“Prasaṅgasādhana is not employed for establishing one’s thesis but for bringing home an undesirable contingency in the opponent’s position. And an undesirable contingency can be brought home by means of the data which are admitted by the opponent himself. It is not necessary that the argument, in order to be valid, should be recognised as valid and true by the arguer himself. The opponent cannot make a grievance of it and refuse to be convinced, though he'himself admits every word of the argument to be true.”[6]

Śāntarakṣita, who is believed to have flourished in tbe 8 th century, and his disciple, Kamalaśīla have made use of prasaṅgānumāna in several places in the Tattvasaṅgraha and the Pañjikā. In course of refuting the Mīmāṃsā argument ‘that the Vedas are eternal and self-evident truths, as they are not the handiwork of any human author,’ Śāntarakṣita points out that the Vedas would become unmeaning, if they were independent of an author, as the truth or falsity of a statement is relative to the veracity or mendacity of the speaker, and the speaker being absent, the truth or otherwise of the Vedic statements would become impossible of ascertainment. Kamalaśīla in his Pañjikā observes in this connexion that the argument (of śāntarakṣita) is a prasaṅgasādhana and not an independent argument:, as the conclusion is obviously contrary to experience (the Vedas having a determinate meaning), and the reason, akartṛkatva (independence of human authorship), is not approved by both the parties. But these two contingencies are allowable in a hypothetical argument of the type of reductio ad absurdum.[7]

The Naiyāyikas, however, do not subscribe to the aforesaid position of the Buddhists. They do not recognise prasaṅgasādhana as a logically justifiable form of argument. They are insistent in their demand that the middle term must be a real datum, attested by experience and approved by both the parties and not a mere hypothetical entity. Any infringement of the above dictum will make the fallacy of ‘unproven middle term’ inevitable. Śaṅkarasvāmin, an older Naiyāyika, emphatically avers that whether the argument be a hypothetical or an independent one, the probans must be attested by one’s own personal experience; otherwise it (the probans) will fail to be appropriate. Kamalaśīla observes that the penalty of the violation of this principle will be the fallacy of unproven middle term.[8]

Jayantabhaṭṭa, the author of the Nyāyamañjarī, has an occasion to speak of prasaṅgasādhana in connexion with his animadversion on Kumārila for his denial of an omniscient yogin. Kumārila declares that even the supersensuous perception of a yogin is not competent to envisage the real nature of dharma (duty).

Jayantabhaṭṭa in opposing Kumārila says,

“If yogic perception be an established fact, your argument is vitiated by Self-contradiction; if it is non-existent, the middle term is unproven in respect of an unreal subject (āśrayāsiddha). You have yourself stated the dictum in rebutting the doctrine of subjective idealism (of the Buddhists) that no inference is possible from unreal data merely on the strength of other people’s belief. And as a (supposed) middle term, accepted only by the adversary, cannot prove the probandum, so also a (supposed) minor term, accepted only by the opponent, is not an acceptable datum.”[9]

“It may be argued that it is a case of prasaṅgasādhana and prasaṅga means the demonstration of a defect in an opponent’s position by means of the data accepted by the latter. But this cannot be approved. Because, prasaṅgasādhana is a form of argument, which is as unreal as a fresco-painting without on a wall. Certainly a dissertation on the fragrance or otherwise of a sky-flower cannot be a justifiable procedure.”[10]

The refusal of the Naiyāyikas to regard prasaṅgānumāna as a valid means of cognition stands on a par with their denial of tarka as an independent means of knowledge. Hemacandra Sūri in his Pramāṇamīmāṃsa and Ratnakīrti in his ‘ Kṣaṇabhaṅgasiddhi’ have elaborately criticised the Naiyāyika position and they have made no scruple to declare that the denial of validity to tarka is due to the cussedness of the Naiyāyika and has. no logic in its support. Without taking sides, we can legitimately hold that prasaṅgasādhana has been wielded as a potent logical weapon in the tangled controversies of the medieval age and is regarded as the only acceptable form of argument by the Mādhyamika school. Whatever be the logical merits of it as a valid syllogistic reasoning, the historical importance of prasaṅga sādhana cannot be underrated by any scrupulous student of Indian thought.[11]

N.B.—I think a word of explanation is necessary for my using the terminology of European logic for elucidating the concepts of Indian logic. There is a fundamental difference between Indian Nyāya and European syllogism in that the former is not content with formal consistency alone, but insists on the material truth of the premises and the conclusion, whereas formal consistency is the only criterion of Aristotelian syllogism.; In fact, the whole controversy in connexion with prasaṅgasādhana would not have arisen st all, if formal consistency had been regarded as the satisfying test of an argument by Indian logicians. But my apology for the use of European terms is that they are the nearest equivalents of Indian logical concepts and in this I have only followed in the footsteps of veteran scholars like the late Dr. Satishcandra Vidyābhūṣaṇa, Dr. Ganganath Jha, Prof. Sir S. Radhakrishnan, Prof Stcherbatsky and others. The readers ore requested to bear this distinction in mind to guard against obvious misunderstanding.


‘sandigdhe’rthe’nyatarapakṣānukūlakāraṇadarśanāt tasmin sambhāvanāpratyayas tarkaḥ.
      N.M., p. 8.


Vide Prof. Radhakrishnan’s Indian Philosophy, Vol. II, p. 114.

Cf. ‘sa cāyaṃ tarko vyāpakābhāvavattvena nirṇite dharmiṇi vyāpyasyā haryāropād vyāpakasyā’hāryāropalakṣaṇaḥ’
      (C. K. Tarkālaṅkāra’s ṭīkā on Nyāya-Kusumāñjali, p. 5)


Vide Nyāyamukha, translated into English from the Chinese version of the same by Prof. G. Tucci. It is gratifying that the present writer’s conjecture has been confirmed, as Dignāga is insistent on the middle term being accepted by common consent.


The Hetutattvopadeśa of Jitāri is lost in the Sanskrit original, but it has been reconstructed from Tibetan by my pupil, Mr. Durgacharan Ghatterjee, M. A., P.R.S. The constructed text with the Tibetan version and copious critical notes and an informing introduction is ready for printing; When published, it would be welcomed as a really ścholarly work.


tataś ca parapratijñāpratiṣedhamātraphalatvāt prasaṅgāpādānasya nāsti prasaṅgaviparyayāpattiḥ. tathā cā’cāryo bhūyasā prasaṅgāpattimukhenai’va paroktāni nirākaroti sma.
      Vide Prasannapadā of Candrakīrti under Kar. I of M. K., p. 6 (B. T. S.).


prasaṅgāpādanañ ca na svapakṣasādhanāyo’pādīyate, kintu parasyā’niṣṭāpādanārtham. parāniṣṭāpādanañ ca tadabhyupagamasiddhair eva dharmādibhiḥ śakyam āpādayitum. tatra pramāṇena avapratītir anapekṣaṇīyā; na hy evam paraḥ pratyavasthātum arhati tavā’siddhā dharmādayo, nā’ham svasiddheṣv api teṣu pratipadya iti.
      N. K., p. 197.


prasaṅgasādhanam etad draṣṭavyam, anyathā hi svātantryeṇa sādhane dṛṣṭavirodhaḥ syāt, tathā hy ‘agnihotraṃ juhuyāt svarga-kāma’ ityādivākyād arthapratītir bhavanty upalabhyata eva, na ca dṛṣṭam apahnotuṃ śakyate, na cā’kartṛkatvaṃ ubhayasiddham ity asiddhaś ca hetuḥ syāt, prasaṅgasādhane tu dvayam apy aduṣṭam.
      T. S. P., p. 487, under śls. 1602-3.


Śaṅkarasvāmin is an older Naiyāyika, who is completely ignored in the Brahmanical works except in the Nyāyamañjarī, where he is referred to only in one place and so would have been totally forgotten but for the quotations of his views in the Tattvasaṅgraha and the Pañjikā. The opinion referred to is embodied in the following verse:

svātantryeṇa prasaṅgena sādhanaṃ yat pravarttate |
svayaṃ tadupalabdhau hi satyāṃ saṅgacchate na tu ||
      T. S., śl. 014.

‘anyathā by asiddhatādoṣaḥ syāt.’ T. S. P., under the above.


parasaṃsiddhamūlam ca nānumānaṃ prakalpate |
uktam bhavadbhir eve’dam nirālmbaanadūṣaṇam ||
sādhyasiddhir yathā nāsti parasiddhena hetunā |
tathai’va dharmisiddhatvaṃ parasiddhyā na yujyate ||
      N.M., p. 102.


tatrai’tat syāt prasaṅgasādhanam idam, prasaṅgaś ca paraprasidddhyā parasyā’niṣṭāpādanam ucyate... nai’tad evam.
prasaṅgasādhanaṃ nāma nasty eva paramārthataḥ |
tad dhi kuḍhyaṃ vinā tatra citrakarme’va lakṣyate ||
na hi nabhaḥkusumasya saurabhāsaurabhavicāro yuktaḥ.
      Nyāyamañjarī, pp. 102-04.


For a convenient understanding of the nature and function of prasaṅgasādhana as an invalidating form of argument we propose to give a concrete illustration in Aristotelian syllogistic form as follows:—

(A) The Mīmāṃsaka’s argument—
All statmentś that have no.authors are infallible.
Vedic statements are those that have no authors.
Vedic statements are infallible.

(B) The Buddhist’s argument—
All statements that have no authors are unmeaning
Vedic statements are those that have no authors.
Vedic statements are unmeaning.

The syllogism (B) is a prasaṅgasādhana in relation to the syllogism (A), as the latter (A) is invalidated by the former (B).