  The concept of doubt has an important theoretical role in Nyāya, for a state of doubt is claimed to be a necessary precondition for any philosophical enquiry. Doubt is one of the sixteen topics listed under Nyāya-sūtra 1.1.1, which determine the content of the entire text. In particular, a doubt is the first step in a properly formulated inference: is there a fire on the mountain?—Yes, because there is smoke there. The Manual of Reason gives a very precise definition of a doubt (TS 71): a cognition of two incompatible qualifiers in the same qualificand, for example the cognition “Is this (dimly perceived or distant object) a person or a tree-stump?” Schematically, then, a doubt is a cognition whose content is of the form “x is F or not-F?”.