ANTHKARANA-CHATUSHTYA (the internal organ quartet): [ಅಂತ:ಕರಣ ಚತುಷ್ಠ್ಯ]

According to the Vachana-writers there are four (chatushtya)[ಚತುಷ್ಠ್ಯ] internal (antar)[ಅಂತರ] instruments (karanās), namely,
Ego (aham)[ಅಹಂ]
Intellect (buddhi) [ಬುದ್ದಿ]
Mind (manasu)[ಮನಸ್ಸು] and
Will (chitta)[ಚಿತ್ತ].
The belief is that the soul makes use of such instruments as legs, hands, etc which are external and mind, intellect, etc. which are internal for its survival and progress. To concentrate on one object at a time is the function of manasu, to determine the nature of the object is the function of buddhi, to know that I know that object is the function of aham, and to decide, wish, etc. is the function of chitta.