Sannikarsha is contact as means of perceptual cognition in Nyaya philosophy. According to the Nyaya School, perceptual cognition arises from sense-object contact. They consider sense organs to be six in number. Some of them are called external and some internal. There is only one internal sense, called manas (mind).
The function of the senses is to produce perception of objects. For a sense organ, to function is to give us immediate knowledge about certain objects. How then, do the senses function to give us perception of objects? Is it through contact or without contact? Sense-object contact (sannikarsha) is a necessary condition. The latter is of six kinds.
A case of direct contact consists in the conjunction (samyoga) between sense and its object. In the visual perception of a substance like the jar, there is an immediate contact of the sense of sight with the object. Secondly, when we see the color of the jar, our sense of sight comes into contact with the jar, our sense of sight comes into contact with the color through the medium of the jar. The jar is conjoined (samyukta) with the visual sense and contains the color as an inherent (samvaya) quality on the other. Hence this sense-object contact is called samyuktasamavaya (a relation of inherence in what is conjoined with sense). This sense-object contact may be more indirect. When by means of the visual sense we perceive a universal, like colorfulness (rupatva), inhering in the jar’s color, there is contact of the visual sense with the object colorfulness through the medium of the two terms jar and color. This contact is called samyukta-samaveta-samavaya.
The fourth case of contact is samavaya (inherence). Here, akasha, which constitutes the auditory sense, has contact with its quality (sound) through the relation of inherence. The last type of sense-object contact is called visesnata or visesanavisesyabhava. In it, the sense is in contact with its object insofar as the object is a qualification (visesana) o another term connected with sense. By means of contact, the Naiyayikas explain the perceptions of non-existence (abhava) and the relation of inherence. Thus it is called samyukta-visesanata when the object is adjectival (visesana) to that which is conjoined (samyukta) to the sense organ.