Despite the twenty-four centuries separating the two men, both Plato and Freud shared the same pessimism regarding human nature: man is driven by his desires or what Freud called ‘drives’ or instincts. The latter was a scientist who firmly believed in the power of rational enquiry. As a father who lost one of his sons in the First World War and who had to leave Austria for England in his old age in order to avoid the systematic anti-Semitic repression of the Nazi regime, it is not altogether surprising that Freud had no illusion as to the moral improvement or progress of the human race. However, Freud always refrained from passing sweeping moral judgements on the human species. He simply hoped that our unique capacity to establish objective knowledge would, one day, enable us to understand our condition and perhaps reduce the causes of our common inner psychological ‘disharmony’, to use a Platonic phrase. Let’s have a look at both Plato and Freud’s division of the psyche:

PLATO                   FREUD
REASON                  EGO
SPIRIT               SUPEREGO

1) The Ego (or the ‘I’, das ‘Ich’) is our conscious self, on display in social situations. For Freud, it ‘represents what we may call reason and common sense.’ Like the charioteer and his two horses in the Phaedrus, the Freudian ego is the rational part of the soul whose task is to reconcile the conflicting interests of both the superego and the id.
2) The Superego (or the ‘Over-I’, das’ Uber-Ich’) is the part of the self influenced by the conditioning of parents, educators and cultural trends. It intervenes in some of the ego’s decisions as its moral conscience. The superego is a social construct shaped by an early identification with the father and his social values. This identification ordinarily turns into an outright rejection of paternal values at the time of adolescence. The superego is the part of the self associated with ambition and social recognition and like Plato’s Spirit, it is essentially about self-respect and self-image as illustrated in the story of Leontion in Book IV of ‘The Republic’ [439e-440a/b].
3) The Id (or the ‘It’, das ‘Es’) is the unconscious, that ‘dark, inaccessible part of our personality’, full of seething passions and desires. For Freud, the unconscious mostly expresses itself through the symbolic language of dreams which both analyst and patient decipher together through the psychoanalytical process. Plato compares man’s multifarious desires to a wild animal, difficult to tame without resorting to ‘divine’ reason (see the analogy of the ‘many-headed beast’ in Book IX [588c-589e].
Plato and Freud are fairly unique in their division of the human psyche into three components. Most classical philosophers, like Descartes, do not introduce a third component in their description of the psyche but divide it between the mind considered as an immaterial substance and the seat of consciousness and the body associated with matter and sensory experience.