It is very probable that the earliest beginnings of Nyaya are to be found in the disputations and debates amongst scholars trying to find out the right meanings of the Vedic texts for use in sacrifices and also in those disputations which took place between the adherents of different schools of thought trying to defeat one another. I suppose that such disputations occurred in the days of the Upani@sads, and the art of disputation was regarded even then as a subject of study, and it probably passed then by the name _vakovakya_. Mr Bodas has pointed out that Apastamba who according to Buehler lived before the third century B.C. used the word Nyaya in the sense of Mima@msa [Footnote ref 399]. The word Nyaya derivedfrom the root _ni_ is sometimes explained as that by which sentences and words could be interpreted as having one particular meaning and not another, and on the strength of this even Vedic accents of words (which indicate the meaning of compound words by pointing out the particular kind of compound in which the words entered into combination) were called Nyaya [Footnote ref 400]. Prof. Jacobi on the strength of Kau@tilya's enumeration of the _vidya_ (sciences) as Anvik@siki (the science of testing the perceptual and scriptural knowledge by further scrutiny), _trayi_ (the three Vedas), _vartta_ (the sciences of agriculture, cattle keeping etc.), and _da@n@daniti_ (polity), and the enumeration of the philosophies as Sa@mkhya, Yoga, Lokayata and Anvik@siki, supposes that the _Nyaya sutra_ was not in existence in Kau@tilya's time 300 B.C.) [Footnote ref 401]. Kau@tilya's reference to Nyaya as Anvik@siki only suggests that the word Nyaya was not a familiar name for Anvik@siki in Kau@tilya's time. He seems to misunderstand Vatsyayana in thinking that Vatsyayana distinguishes Nyaya from the Anvik@siki in holding that while the latter only means the science of logic the former means logic as well as metaphysics. What appears from Vatsyayana's statement in _Nyaya sutra_ I.i. 1 is this that he points out that the science which was known in his time as Nyaya was the same as was referred to as Anvik@siki by Kau@tilya. He distinctly identifies Nyayavidya with Anvik@siki, but justifies the separate enumeration of certain logical categories such as _sa@ms'aya_ (doubt) etc., though these were already contained within the first two terms _prama@na_ (means of cognition) and _prameya_ (objects of cognition), by holding that unless these its special and separate branches (_p@rthakprasthana_) were treated, Nyayavidya would simply become metaphysics (_adhyatmavidya_) like the Upani@sads. The old meaning of Nyaya as the means of determining the right meaning or the right thing is also agreed upon by Vatsyayana and is sanctioned by Vacaspati in his _Nyayavarttikatatparya@tika_ I.i. 1). He compares the meaning of the word Nyaya (_prama@nairarthaparik@sa@nam_--to scrutinize an object by means of logical proof) with the etymological meaning of the word anvik@siki (to scrutinize anything after it has been known by perception and scriptures). Vatsyayana of course points out that so far as this logical side of Nyaya is concerned it has the widest scope foritself as it includes all beings, all their actions, and all the sciences [Footnote ref 402]. He quotes Kau@tilya to show that in this capacity Nyaya is like light illumining all sciences and is the means of all works. In its capacity as dealing with the truths of metaphysics it may show the way to salvation. I do not dispute Prof. Jacobi's main point that the metaphysical portion of the work was a later addition, for this seems to me to be a very probable view. In fact Vatsyayana himself designates the logical portion as a p@rthakprasthana (separate branch). But I do not find that any statement of Vatsyayana or Kau@tilya can justify us in concluding that this addition was made after Kau@tilya. Vatsyayana has no doubt put more stress on the importance of the logical side of the work, but the reason of that seems to be quite obvious, for the importance of metaphysics or _adhyatmavidya_ was acknowledged by all. But the importance of the mere logical side would not appeal to most people. None of the dharmas'astras (religious scriptures) or the Vedas would lend any support to it, and Vatsyayana had to seek the support of Kau@tilya in the matter as the last resource. The fact that Kau@tilya was not satisfied by counting Anvik@siki as one of the four vidyas but also named it as one of the philosophies side by side with Sa@mkhya seems to lead to the presumption that probably even in Kau@tilya's time Nyaya was composed of two branches, one as adhyatmavidya and another as a science of logic or rather of debate. This combination is on the face of it loose and external, and it is not improbable that the metaphysical portion was added to increase the popularity of the logical part, which by itself might not attract sufficient attention. Mahamahopadhyaya Haraprasada S'astri in an article in the _Journal of the Bengal Asiatic Society_ 1905 says that as Vacaspati made two attempts to collect the _Nyaya sutras_, one as _Nyayasuci_ and the other as _Nyayasutroddhara_, it seems that even in Vacaspati's time he was not certain as to the authenticity of many of the _Nyaya sutras_. He further points out that there are unmistakable signs that many of the sutras were interpolated, and relates the Buddhist tradition from China and Japan that Mirok mingled Nyaya and Yoga. He alsothinks that the sutras underwent two additions, one at the hands of some Buddhists and another at the hands of some Hindu who put in Hindu arguments against the Buddhist ones. These suggestions of this learned scholar seem to be very probable, but we have no clue by which we can ascertain the time when such additions were made. The fact that there are unmistakable proofs of the interpolation of many of the sutras makes the fixing of the date of the original part of the _Nyaya sutras_ still more difficult, for the Buddhist references can hardly be of any help, and Prof. Jacobi's attempt to fix the date of the _Nyaya sutras_ on the basis of references to S'unyavada naturally loses its value, except on the supposition that all references to S'unyavada must be later than Nagarjuna, which is not correct, since the _Mahayana sutras_ written before Nagarjuna also held the S'unyavada doctrine.
The late Dr S.C. Vidyabhu@sa@na in _J.R.A.S._ 1918 thinks that the earlier part of Nyaya was written by Gautama about 550 B.C. whereas the _Nyaya sutras_ of Ak@sapada were written about 150 A.D. and says that the use of the word Nyaya in the sense of logic in _Mahabharata_ I.I. 67, I. 70. 42-51, must be regarded as interpolations. He, however, does not give any reasons in support of his assumption. It appears from his treatment of the subject that the fixing of the date of Ak@sapada was made to fit in somehow with his idea that Ak@sapada wrote his _Nyaya sutras_ under the influence of Aristotle--a supposition which does not require serious refutation, at least so far as Dr Vidyabhu@sa@na has proved it. Thus after all this discussion we have not advanced a step towards the ascertainment of the date of the original part of the Nyaya. Goldstuecker says that both Patanjali (140 B.C.) and Katyayana (fourth century B.C.) knew the _Nyaya sutras_ [Footnote ref 403]. We know that Kau@tilya knew the Nyaya in some form as Anvik@siki in 300 B.C., and on the strength of this we may venture to say that the Nyaya existed in some form as early as the fourth century B.C. But there are other reasons which lead me to think that at least some of the present sutras were written some time in the second century A.D. Bodas points out that Badaraya@na's sutras make allusions to the Vais'e@sika doctrines and not to Nyaya. On this ground he thinks that _Vais'e@sika sutras_ were written before Badarayana's _Brahma-sutras_, whereas the Nyaya sutras were written later. Candrakanta Tarkala@mkara also contends in hisedition of Vais'e@sika that the _Vais'e@sika sutras_ were earlier than the Nyaya. It seems to me to be perfectly certain that the _Vais'e@sika sutras_ were written before Caraka (80 A.D.); for he not only quotes one of the _Vais'e@sika sutras_, but the whole foundation of his medical physics is based on the Vais`e@sika physics [Footnote ref 404]. The _La@nkavatara sutra_ (which as it was quoted by As'vagho@sa is earlier than 80 A.D.) also makes allusions to the atomic doctrine. There are other weightier grounds, as we shall see later on, for supposing that the _Vais'e@sika sutras_ are probably pre-Buddhistic [Footnote ref 405].
It is certain that even the logical part of the present _Nyaya sutras_ was preceded by previous speculations on the subject by thinkers of other schools. Thus in commenting on I.i. 32 in which the sutra states that a syllogism consists of five premisses (_avayava_) Vatsyayana says that this sutra was written to refute the views of those who held that there should be ten premisses [Footnote ref 406]. The _Vais'e@sika sutras_ also give us some of the earliest types of inference, which do not show any acquaintance with the technic of the Nyaya doctrine of inference [Footnote ref 407].