Tarka or logic, which depends upon ūhā or guessing, is one of the aids to attaining correct knowledge when direct and clear knowledge is not possible. Philosophical treatises often take recourse to it.
As far as the spiritual truths beyond the ken of the senses are concerned, tarka is not accepted as an independent source of knowledge. It is accepted only if it does not go against the Śruti (Vedas) but strengthens its teachings.
The word tarka is also used in the sense of Tarkaśāstra or the Science of Logic. The Nyāya and the Vaiśeṣika schools are generally considered Tarka-śāstras. There are also independent works on the same subject.
Tarka as logical reasoning can be proved with a simple illustration. When we notice smoke rising from a nearby hillock, we conclude that there is a fire on it though we do not actually see the fire itself. This is because, in our prior experience, we have observed that wherever there had been smoke, there was a fire also. If someone argues that smoke may be there even without fire, the reply is that it cannot be, since smoke and fire have always gone together. This is a universal experience. This method of proving is tarka.
Works on tarka have described eleven varieties of the same. They are: anavasthā, anyonyāśraya, apavāda, ātmāśraya, cakraka, kalpanāgaurava, kalpanā-lāghava, pratibandhikalpanā, utsarga, vaijātya and vyāghāta. (See under each title for details.)