Taboo restrictions are distinct from religious or moral prohibitions. They are not based upon any divine ordinance, but may be said to impose themselves on their own account. They differ from moral prohibitions in that they fall into no system that declares quite generally that certain abstinences must be observed and gives reasons for that necessity.

The Standard Edition of the Complete Psychological Works of Sigmund Freud: (1913-1914) Totem and taboo and other works. [1955 (ed. 1953)