Y. Keshava Menon

“The antahkarana is ever active and assumes various forms or ‘modes’ — except in deep sleep, when its activity is latent in itself. One of its modes is the consciousness of itself, which may be called ‘ego-hood’. The ego commonly confuses itself with the real Self. ‘When we say ‘I am restless’, we mean that the antahkarana is restless, but we wrongly transfer the restlessness to our inner Self. Herein lies the essential difference between mere introspection and the knowledge of the inner divine Self, which comes from knowing this philosophy as Shankara knew it. Knowing his philosophy and knowing ‘about’ it are on two different planes. When the antahkarana assumes the mode of doubt or indetermination, it is called ‘mind’ — in the sense used in the statement ‘I cannot make up my ‘mind’. The item ‘mind’ includes resolution, sense-perception, desires and emotions. When the antahkarana has the mode of certainty or determination, it may be called ‘intellect’, including the powers of judgment and reasoning; and when in the mode of reflection and remembrance, it may be called ‘attention’. The ego, the mind, and the intellect function only intermittently; their activity has a birth, growth and death. An argument, for example, begins with the premises and works through a chain of reasoning to a conclusion. ‘Attention’, however, may endure; and this mode of the antahkarana is regarded as the most important, because meditation, contemplation and concentration belong to its province, and these are the activities by which a person uses his antahkarana to seek and find Reality. They are the point of the thorn used to extract the other thorn of avidya.”
― Y. Keshava Menon, The Mind of Adi Shankaracharya

“I’ can denote: (1) the inner consciousness, or knower; (2) the ‘antahkarana’, or ‘inner organ’; (3) the ego; (4) the ‘jiva’, or soul.”
― Y. Keshava Menon, The Mind of Adi Shankaracharya