Freud proposed in Beyond the Pleasure Principle (1920b) a ‘death instinct’ (Thanatos) as an equal partner in the unconscious with the libido or life instinct (Eros). The death instinct manifested itself as destructive aggression, a force in the psyche which endeavored to destroy or dissolve all the integrated ‘unities’ that Eros strove to create.
Kalsched provides the foundational Freudian formulation: Thanatos as the psychic force opposed to and equal with Eros, tracing the dualism to Empedocles and linking it clinically to primary masochism and superego sadism.
, The Inner World of Trauma: Archetypal Defences of the Personal Spirit, 1996thesis