Psychoanalytic theorists have proposed that human behaviour is deterministic, and is governed by irrational forces, in the form of unconscious and instinctual and biological drives. Sigmund Freud proposed that the personality consists of three different elements: the Id, the Ego and the Superego. Psychosexual development is a central element of the psychoanalytic sexual drive theory, which states that human beings, from birth, possess an instinctual libido (sexual energy) that develops in five stages: the oral, the anal, the phallic, the latent, and the genital.