According to freud, two instincts furnish the energy for personality functioning. these instincts are

The answer is sex and aggression. Freud's view on sex and aggression that these are the strong innate forces in psychologic system. He called these as instinct. Freud postulated that human have a fundamental instinct towards destruction and this instinct is manifested through aggression. This is referred sometimes as the life instinct or libido and thanatos for death instinct. He also used the term libido to the need to satisfy, sustain life and pleasure related urge. He also note that this can occur in combination in various ways and situations.