argued that there may always be certain unknown conditions which may vitiate the validity of inference.  To this Vacaspati’s answer is that if even after observing a large number of cases and careful search such conditions (upadhi) cannot be discovered, we have to take it for granted that they do not exist and that there is a natural connection between the middle and the major.  The later Buddhists introduced the method of Pancakara@ni in order to determine effectively the causal relation.  These five conditions determining the causal relation are (1) neither the cause nor the effect is perceived, (2) the cause is perceived, (3) in immediate succession the effect is perceived, (4) the cause disappears, (5) in

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[Footnote 1:  Karyyakara@nubhavadva svabhavadva niyamakat avinabhavaniyamo’ dars’ananna na dars’anat.  Tatparya@tika, p. 105.]

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immediate succession the effect disappears.  But this method cannot guarantee the infallibility of the determination of cause and effect relation; and if by the assumption of a cause-effect relation no higher degree of certainty is available, it is better to accept a natural relation without limiting it to a cause-effect relation [Footnote ref 1].

In early Nyaya books three kinds of inference are described, namely purvavat, s’e@savat, and samanyato-d@r@s@ta.  Purvavat is the inference of effects from causes, e.g. that of impending rain from heavy dark clouds; s’e@savat is the inference of causes from effects, e.g. that of rain from the rise of water in the river; samanyato-d@r@s@ta refers to the inference in all cases other than those of cause and effect, e.g. the inference of the sour taste of the tamarind from its form and colour. Nyayamanjari mentions another form of anumana, namely paris’e@samana (reductio ad absurdum), which consists in asserting anything (e.g. consciousness) of any other thing (e.g. atman), because it was already definitely found out that consciousness was not produced in any other part of man.  Since consciousness could not belong to anything else, it must belong to soul of necessity.  In spite of these variant forms they are all however of one kind, namely that of the inference of the probandum (sadhya) by virtue of the unconditional and invariable concomitance of the hetu, called the vyapti-niyama.  In the new school of Nyaya (Navya-Nyaya) a formal distinction of three kinds of inference occupies an important place, namely anvayavyatireki, kevalanvayi, and kevalavyatireki.  Anvayavyatireki is that inference where the vyapti has been observed by a combination of a large number of instances of agreement in presence and agreement in absence, as in the case of the concomitance of smoke and fire (wherever there is smoke there is fire (anvaya), and where there is no fire, there is no smoke (vyatireka)).