Complex sentence: Id, ego, and super-ego are the three parts of the psychic apparatus defined in Sigmund Freud's structural model of the psyche; they are the three theoretical constructs in terms of whose activity and interaction our mental life is described.
Split into simpler sentences: Id, ego, and super-ego are the three parts of the psychic apparatus defined in Sigmund Freud's structural model of the psyche. The three parts are the theoretical constructs in terms of whose activity and interaction our mental life is described.