The word Nyaya has a number of meanings in Sanskrt, "an original type, or that into which a thing goes back; a plan, system; a logical argument; etc."; and Nyaya, coming after the Sankhya, may be said to give us a pattern of thought which serves as a model for all other systems. There is an undoubted plan underlying the sixty topics of the Sankhya; but its treatment of the problems of life is not exactly systematic, and it keeps true to its own type, as indicated by its name.
Nyaya, on the other hand, though limited in its scope, is more systematic. The Sankhya emphasizes the importance of knowledge as a means of attaining to freedom from pain; and Nyaya tells us what kind of knowledge this should be. The highest happiness, it tell us in the opening Sutra of the work, arises from a knowledge of the essence of sixteen "categories" of things; and the rest of it is devoted to an examination of each one of them. It is divided into five chapters, with two parts to each chapter; and the subject-matter of the sixteen "categories" is divided among them.
The plan of the whole work is simple in the extreme. The first Sutra of the first part of the first chapter tells us what these sixteen "categories" are; and the next Sutra tells us that the freedom of the soul arises when pain, natural activity, and faults arising from false knowledge disappear; and the remaining part of the whole chapter, with both its parts, is devoted to a definition of terms used in connection with these "categories".
The first of these "categories" relates to the means of acquiring knowledge; and the first part of the second chapter is devoted to a detailed examination of the principal means, while the second part deals with some other problems of acquiring knowledge. The second "category" relates to the objects to be known, which are said to be twelve in number; and the first part of the third chapter deals with four, and the second part with three more, of these.
In the first part of the fourth chapter the remaining five of these "objects" are dealt with; and then the author goes on to consider ten out of the fourteen remaining "categories" in the second part of this chapter. In the first part of the fifth chapter three more out of the remaining four "categories" are dealt with; while the second part of this chapter ends with an examination of the last "category". The text may now be summarized as follows:-
The sixteen categories; the definition of terms: The highest happiness arises from knowledge of the sixteen "categories" of things; and the freedom of the soul arises when pain, natural activity, and faults arising from false knowledge disappear. There are four means of acquiring knowledge; and the objects to be proved are twelve in number. In the same manner we may define some more "categories" of things.
The subject matter of Nyaya: The highest happiness arises from a knowledge of the essence of sixteen "categories" of things: (1) the means of acquiring knowledge; (2) the objects to be known; (3) doubt; (4) motive or purpose in action; (5) instances; (6) admitted or established truth; (7) different parts of an argument or syllogism; (8) the process of reasoning; (9) the art of drawing conclusions; (10) discussion; (11) disputation; (12) carping criticism; (13) fallacies; (14) quibbles; (15) the real nature of things; and (16) inability to carry on an argument because of impossibility of agreement on the first principles.
The freedom of the soul: The freedom of the soul arises, when pain, natural activity, and faults arising from false knowledge disappear.
The means of acquiring knowledge: There are four means of acquiring knowledge, sense-perception, inference, analogy or instances, and testimony of the trustworthy and the wise. The Sankhya gives us only three means of acquiring knowledge, sense-perception, inference, and testimony of the trustworthy and the wise. Nyaya adds one more, analogy or instances.
The objects to be proved: The objects to be proved are twelve in number, (1) soul; (2) body; (3) senses; (4) objects of the senses; (5) intellect; (6) mind; (7) activity; (8) faults; (9) state after death; (10) fruit of action; (11) pain; and (12) emancipation of the soul.
Doubt: Doubt arises from a peculiar connection of cause and effect, a number of similar perceptions, contradictions, and irregularities of perception and non-perception.
Purpose in action: Purpose in action is the aim that causes action.
Instances: An instance is that which enables common people to understand a thing in the same manner as an expert.
An admitted truth: An admitted truth means complete agreement in regard to an essential principle. It is of two kinds, universal and particular. A universal established truth is that in which each part of an idea or object is consistent with all its essential parts. A particular established truth is that which can be conclusively proved in connection with a similar idea too. An established truth by agreement is that which has been accepted after special examination.
Different parts of a syllogism: There are five parts of a syllogism: (a) a statement of the proposition; (b) reason for the statement; (c) illustration; (d) drawing near to the conclusion; and (e) conclusion.
The process of reasoning: The process of reasoning is an examination of an object in order to understand its course of nature or character.
The art of drawing conclusions: The art of drawing conclusions consists in making a definite statement about an object after examining it from all sides.
Discussion: Discussion consists in a criticism of the means of acquiring knowledge, reasoning and proof.
Disputation: Disputation includes all that is contained in discussion; and it is a censurable form of giving expression to quibbles, the real nature of a thing, and inability to carry on an argument for want of agreement on the first principles.
Carping criticism: Carping criticism consists in taking up a very strong attitude on the opposite side.
Fallacies: A fallacy consists in an argument which is wide of the mark, is inconsistent, is identical with the question itself, is similar to the thing to be proved, or is untimely, that is, when the reason for it has ceased to be applicable.
Quibbles: Quibbling consists in so breaking up the language of a statement as to produce a doubt in regard to its meaning. It is of three kinds; perverting the sense of language, of fundamental notions, and of the mode of treatment of the question.
The real nature of a thing: The real nature of a thing consists in understanding its original or essential nature from similar as well as dissimilar characteristics.
Inability to carry on an argument from impossibility of agreement on the first principles: Inability to carry on an argument from impossibility of agreement on the first principles consists in erroneous notions and want of understanding; and it is of many kinds.