The whole of the fifth book which seems to be a later addition is devoted to the enumeration of different kinds of refutations (nigrahasthâna) and futilities (jâti).
Caraka, Nyâya sûtras and Vais'e@sika sûtras.
When we compare the Nyâya sûtras with the Vais'e@sika sûtras we find that in the former two or three differentstreams of purposes have met, whereas the latter is much more homogeneous. The large amount of materials relating to debates treated as a practical art for defeating an opponent would lead one to suppose that it was probably originally compiled from some other existing treatises which were used by Hindus and Buddhists alike for rendering themselves fit to hold their own in debates with their opponents [Footnote ref 2]. This assumption is justified when
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[Footnote 1: Vâtsyâyana notes that this is the salvation of him who has known Brahman, IV. i. 63.]
[Footnote 2: A reference to the Suvar@naprabhâsa sûtra shows that the Buddhist missionaries used to get certain preparations for improving their voice in order to be able to argue with force, and they took to the worship of Sarasvatî (goddess of learning), who they supposed would help them in bringing readily before their mind all the information and ideas of which they stood so much in need at the time of debates.]
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we compare the futilities (jâti) quibbles (chala), etc., relating to disputations as found in the Nyâya sûtra with those that are found in the medical work of Caraka (78 A.D.), III. viii. There are no other works in early Sanskrit literature, excepting the Nyâya sûtra and Caraka-sa@mhitâ which have treated of these matters. Caraka's description of some of the categories (e.g. d@r@s@tânta, prayojana, pratijñâ and vita@n@dâ) follows very closely the definitions given of those in the Nyâya sûtras. There are others such as the definitions of jalpa, chala, nigrahasthâna, etc., where the definitions of two authorities differ more. There are some other logical categories mentioned in Caraka (e.g. prati@s@thâpanâ, jijñâsâ, vyavasâya, vâkyado@sa, vâkyapras'a@msâ, upalambha, parihâra, abhyanujñâ, etc.) which are not found in the Nyâya sûtra [Footnote ref 1]. Again, the various types of futilities (jâti) and points of opponent's refutation (nigrahasthâna) mentioned in the Nyâya sûtra are not found in Caraka. There are some terms which are found in slightly variant forms in the two works, e.g. aupamya in Caraka, upamâna in Nyâya sûtra, arthâpatti in Nyâya sûtra and arthaprâpti in Caraka. Caraka does not seem to know anything about the Nyâya work on this subject, and it is plain that the treatment of these terms of disputations in the Caraka is much simpler and less technical than what we find in the Nyâya sûtras. If we leave out the varieties of jâti and nigrahasthâna of the fifth book, there is on the whole a great agreement between the treatment of Caraka and that of the Nyâya sûtras. It seems therefore in a high degree probable that both Caraka and the Nyâya sûtras were indebted for their treatment of these terms of disputation to some other earlier work. Of these, Caraka's compilation was earlier, whereas the compilation of the Nyâya sûtras represents a later work when a hotter atmosphere of disputations had necessitated the use of more technical terms which are embodied in this work, but which were not contained in the earlier work. It does not seem therefore that this part of the work could have been earlier than the second century A.D. Another stream flowing through the Nyâya sûtras is that of a polemic against the doctrines which could be attributed to the Sautrântika Buddhists, the Vijñânavâda Buddhists, the nihilists, the Sâ@mkhya, the Cârvâka, and some other unknown schools of thought to which we find no
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[Footnote 1: Like Vais'e@sika, Caraka does not know the threefold division of inference (anumâna) as pûrvavat, s'e@savat and sâmânyatod@r@s@ta.]