  ‘Semantic fitness’ (yogyatā) is an intriguing concept. The Manual of Reason defines it as ‘the absence of incompatibility among what is signified by the words’, and illustrates its definition by contrasting the sentence “He sprinkles the field with water” with “He sprinkles the field with fire”. The idea is that the activity of sprinkling is ‘compatible with’ (i.e. can only be done with) a liquid like water, and not with a substance like fire. It would be like saying “Cathood is on the mat” or perhaps Chomsky’s “Colourless green ideas sleep furiously”. Such sentences, though grammatically correct, do not make sense. This causal factor, then, is that an utterance is intelligible only if the proposition expressed is ontologically possible, by the light of a preconceived ontological system, such as the Vaiśeṣika system of categories. Some Naiyāyikas, however, impose a more demanding requirement, that to be ‘semantically fit’ the utterance must be true, i.e. that ‘fit’ = ‘true’, not merely ‘possible’, and consequently that an utterance is intelligible only if it is true! In effect, they identify ‘semantic fitness’ with the ‘guṇa’ or ‘causal factor leading to truth’, in the language-processing mechanism. We will return to this dispute a little later.