The word 'ego' has had a long and chequered history. To theologians it was the soul—a homunculus within the man—a concept which Roheim has exposed as an introjected phallus, but which still survives, in a vaguer form, in the writings of metaphysicians and even of psychologists. Meanwhile, Hume and his followers identified it, more usefully, with the stream of consciousness, that is, with the impressions, ideas and feelings that compose a mental life. To metapsycho-analysts like Federn, however, the word has both a wider and narrower scope. According to their usage, part of the ego is unconscious and part of consciousness is outside the ego. It