One of the six philosophical schools of Hinduism, Nyaya became established between 6th century BCE and 2nd century BCE. The foundational text of this school, the Nyaya Sutras, was composed in this period by Akṣapada Gautama whose exact dates are not certain. It is possible that several scholars may have made contributions to the Nyaya Sutras. One of the achievements of the Nyaya school is that they developed a method based on specific rules of reasoning through which certain knowledge of a particular object of inquiry can be achieved.
According to the Nyaya school, an enquiry can be undertaken only if there are some doubts about the nature of what is being enquired into. This means that there is no point in enquiring about something for which certain knowledge is already available. What is being enquired into has to be something about which there is lack of understanding. The availability of some kind of observational data on the basis of which the inquiry will be conducted is another important consideration that the enquirer has to consider. The insistence on observational data shows that the Nyaya school gave importance to the empirical world.
The enquirer has to ensure that there is a possibility of attaining certain knowledge at the end of the enquiry. If certain knowledge is impossible, then conducting an enquiry is a futile exercise. However, doubt and the possibility of certain knowledge are not the only criteria on the basis of which an enquiry can be undertaken. Gautama insists that an enquiry should not be undertaken for flimsy reasons—there has to be a valid purpose to justify the exercise. He notes that an enquiry is meant to contribute to the highest good.