Viññāna: 'consciousness', is one of the 5 groups of existence aggregates or clusters;khandha, one of the 4 nutriments āhāra, the 3rd link of the dependent origination paticcasamuppāda, the 5th in the sixfold division of elements; dhatu.
Viewed as one of the 5 groups; khandha it is inseparably linked with the 3 other mental groups feeling, perception and constructions and furnishes the bare cognition of the object, while the other 3 contribute more specific functions. Its ethical and kammic character, and its greater or lesser degree of intensity and clarity, are chiefly determined by the mental constructions associated with it.
Just like the other groups of existence, consciousness is a flux viññāna-sotā, stream of c.' and does not constitute an abiding mind-substance; nor is it a transmigrating entity or soul. The 3 characteristies see: ti-lakkhana impermanence, suffering and no-self, are frequently applied to it in the texts e.g., in the Anattalakkhana Sutta, S.XXII, 59. The Buddha often stressed that;apart from conditions, there is no arising of consciousness' M 38; and all these statements about its nature hold good for the entire range of consciousness, be it;past, future or presently arisen, gross or subtle, in oneself or external, inferior or lofty, far or near; see: XXII, 59.
According to the 6 senses it divides into 6 kinds, viz. eye or visual consciousness cakkhu-v etc. About the dependent arising of these 6 kinds of consciousness, Vis.M XV, 39 says: 'Conditioned through the eye, the visible object, light and attention, visual-consciousness arises. Conditioned through the ear, the audible object, the ear-passage and attention, ear-consciousness arises. Conditioned, through the nose, the olfactive object, air and attention, nose-consciousness arises. Conditioned through the tongue, the gustative object, humidity and attention, tongue-consciousness arises. Condlitioned through the body, bodily contact, the earth-element and attention, body-consciousness arises. Conditioned through the subconscious mind bhavanga-mano the mental-object and attention, mind-consciousness arises
The Abhidhamma literature distinguishes 89 crasses of consciousness, being either kammically advantageous, disadvantageous or neutral, and belonging either to the sense-sphere, the fine-material or the immaterial sphere, or to supra-mundane consciousness.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.