Symbiosis, in a psychological sense, means the union of one individual self with another self (or any other power outside of the own self) in such a way as to make each lose the integrity of its own self and to make them completely dependent on each other. ― (1941a: Escape from Freedom, New York (Farrar and Rinehart) 1941, p. 158)
„Dependency“ presupposes the clear distinction between two persons, one of whom is dependent on the other. In the case of a symbiotic relationship the symbiotically attached person may sometimes feel superior, sometimes inferior, sometimes equal to the host person―but always they are inseparable. Actually, this symbiotic unity can best be exemplified by mentioning the unity of the mother with the fetus. Fetus and mother are two, and yet they are one. It happens also, and not too rarely, that both persons involved are symbiotically attached, each to the other. In this case one is dealing with a folie à deux, which makes the two unaware of their folie because their shared system constitutes reality for them. In the extremely regressive forms of symbiosis the unconscious desire is actually that of returning to the womb. ― (1964a: The Heart of Man. Its Genius for Good and Evil, New York (Harper and Row) 1964, pp. 104f.)