Nyāya Sūtras 4

And the procedure of this treatise is threefold: enunciation, definition, and critical examination. Among these, enunciation is the statement of a mere category by name.

Among these, definition is the property that differentiates the real nature of what has been enunciated. Critical examination is the determination through means of valid cognition whether what has been defined is tenable according to its definition or not. There, the definition of what has been enunciated and classified is stated,

as in the case of the means of valid cognition and of the object of valid cognition. The statement of division of what has been enunciated and defined [is also given], as in the case of quibble: "Quibble is the obstruction of a statement by assuming an alternative meaning," [and] "It is of three kinds." Now, the statement of division of what has been enunciated:

Nyāyasūtra 1.1.3: Perception, inference, comparison, and verbal testimony are the means of valid cognition.

Perception is the functioning of each sense organ with respect to its corresponding object. But that functioning is contact, or cognition.

When it is contact, then cognition is the valid cognition; when it is cognition, then the cognitions of avoidance, acquisition, and indifference are the result.

Inference: inference is measuring [cognizing] after the object possessing the mark, by means of the mark that has been measured [cognized].

Comparison is knowledge of proximity, as [in the example]: 'as the cow, so the wild ox'. But proximity is the possession of commonality. Verbal testimony: by this an object is spoken [śabdyate]—that is to say, it is designated, made known.

The means of valid cognition are to be understood as the instruments of apprehension through the force of the etymological explanation of their general name. For the word 'pramāṇa' [means of valid cognition] designates an instrument, in the sense that 'an object is cognized [pramīyate] by this.' The explanation of the names of its particular [varieties] is also just like that. But do the means of valid cognition converge on the same object of valid cognition? Or are they restricted to distinct objects of valid cognition?

Both [cases] are observed. The self is cognized from authoritative instruction: "The self exists"; inference regarding it is: "Desire, aversion, effort, pleasure, pain, and knowledge are the inferential marks of the self"; perception [of it] is: "The self is perceptible to one engaged in yoga, born of meditative concentration, due to a specific contact between the self and the internal organ." Fire is cognized from authoritative instruction: "Here is fire"; it is inferred by one approaching by the sight of smoke; and it is apprehended through perception by one who is near. Restriction, however, [is as follows]: "One desiring heaven should perform the agnihotra sacrifice"—for an ordinary person there is neither observation of an inferential mark nor perception regarding heaven. When the sound of thunder is heard, there is inference of the cause of the sound; regarding that, there is neither perception nor testimony. When [an object] is perceived right in one's hand, there is neither inference nor testimony.
And this valid cognition culminates in perception. Comprehending a desired object from authoritative instruction, one wishes to know it also through the observation of an inferential mark;

and having inferred it from the observation of an inferential mark, one desires to see it through perception. When the object is apprehended, the desire to know ceases. The example mentioned earlier is "fire". For the cognizer, the co-occurrence of means of valid cognition is confluence, while their non-co-occurrence is restriction. || 3

Thus ends the commentary on the triad of aphorisms.