Austrian psychoanalyst Sigmund Freud's Civilizations and its Discontents (1930) is one of the most important texts of the twentieth century and is read across disciplines ranging from psychology to literature to sociology. It remains a foundational text in the field of psychology. In this text, Freud discusses the what has become a famous concept of the superego, the ego, and the id. He also discusses the unique relationship between sexual love and family love.

In chapter 4, Freud writes:

People give the name 'love' to the relationship between a man and a woman whose genital needs have led them to found a family; but they also give the name 'love' to positive feelings between parents and children, and between brothers and sisters of a family, although we are obliged to describe this as 'aim-inhibited' love or 'affection'.

Freud (quite controversially but compellingly) claims that this sort of love was originally fully sensual and is still sensual in man's unconscious. There are advantages, according to Freud, of inhibiting this sexual love. For example, "aim-inhibited" love leads individuals to form friendships. They are immune from the bonds of exclusivity. Therefore, friendship is quite valuable from a cultural standpoint. The sexual love, of course, leads to the formation of new families. Both types of love lead the individual outside of the family to form bonds with former strangers. This distinction of love, and moreover the relationship between the two types of love, is a touchstone argument of Freud's, and one that has contributed to his lasting notoriety.

In chapter 7, Freud writes:

The commandment to 'Love thy neighbor as thyself' [is] the strongest defense against human aggressiveness, and an excellent example of the unpsychological proceedings of the super-ego. The command is impossible to fulfill; such an enormous inflation of love can only lower its value, not get rid of the difficulty.

This quote demonstrates Freud's direct engagement with, and rejection of, an important tenet of Christian doctrine. His categorical rejection of this widely regarded Christian commandment produces a surprising result: that to love one's neighbor is actually prone to inhibit the development of civilization, which must insist that individuals defend against neighbors.

What does civilization employ in order to inhibit the aggressiveness that opposes it, to make it harmless, get rid of it perhaps? . . . This we can study in the development of the individual. What happens in him to render his desire for aggression innocuous? Something very remarkable, which we should never have guessed, and which is nevertheless quite obvious. His aggressiveness in introjected; internalized; it is, in point of fact, sent back to where it came from—that is, directed toward his own ego. (Ch. 6)

In the above quote, Freud proposes a unique definition of guilt: that is, internally directed aggression with no other outlet. The super-ego, by means of human conscience, feels guilt as a result of not having recourse to satisfy this instinct for aggression upon others.

Elsewhere, Freud states that

. . . besides the instinct to preserve the living substance and join it into ever larger units, there must exist another, contrary instinct to dissolve those units and bring them back to their primeval, organic state. That is to say, as well as Eros, there must be an instinct of death. (Ch. 6)

The instinct to love (Greek: Eros) and the instinct for death (Thanatos) are two competing impulses that are, according to Freud, present in all individuals, as well as all societies. These impulses, therefore, govern relationships among individuals and among societies.