Jnana lakshana pratyasatti is one of the alaukika pratyaksha – non-sensual perception of things. Alaukika pratyaksha is perception through extraordinary (in contrast to the ordinary) channels, i.e. not through the senses. This concept seems to be the contribution of the Naiyayikas (logicians), beginning with Gangesha Upadhyaya. Three kinds of extraordinary perception have been identified – samanya lakshana pratyasatti, jnana lakshana pratyasatti and yogaja.
Jnana lakshana pratyasatti is a non-sensual perception of an object through previous knowledge of the object. When one sees a piece of sandalwood through normal sense-contact, he says not only “I see sandalwood” but also, “I see a fragrant sandalwood”. Here the fragrance is not in sense-contact and is much less seen. It is only remembered as invariably present in sandalwood. Hence we must admit that there is an extraordinary contact of fragrance with the eye, brought about by the memory of the fragrance in sandalwood.
While in samanya lakshana, the knowledge of the universal inherent in a particular object given in ordinary perception leads directly to the knowledge of all cases of that object as a class, in the jnana lakshana the past experience gives us the extraordinary direct perception of the quality like fragrance inhering in the object perceived by normal sense-channel (yadvishayakam jnanam tasyaiva pratyasattih).
Illusions are accounted for by the Naiyayikas through the jnana lakshana. When shell is mistaken for silver, this illusory silver is perceived here and now by the force of the memory of real silver perceived in the past elsewhere through normal sense-channel.