In the Three Essays on the Theory of Sexuality, written in 1905, Sigmund Freud saw the anxiety of separation as a special case of anxiety based on the phenomenon of "unused libido." The absence of the mother (due to separation) prevented the infant from binding its affects to the maternal representation and it was these affects, together with their libidinal energy, that were transformed into anxiety. Otto Rank (1924) saw anxiety as rooted in the trauma of birth, which constitutes the quintessential separation experience (biologically, in fantasy, etc.).
In Inhibitions, Symptoms and Anxiety (Freud, 1926d ), which, to a large extent, is a response to the position taken by Otto Rank two years earlier, Freud developed the theory of signal anxiety, which represents a kind of evolutionary progress since it involves anticipatory behavior. The infant no longer experiences anxiety when faced with the loss of an object but when faced with the fear of the loss of love from the object. There Freud developed different models of anxiety that, rather than being mutually exclusive, probably refer to different types of anxiety and different maturational steps. The conceptual transition from automatic anxiety to signal anxiety involves a profound reworking of his thinking about repression. In the case of automatic anxiety Freud made anxiety a direct consequence of repression. Repression, by ejecting the instinctual representation from consciousness, leaves a certain amount of libido unused, which is immediately transformed into anxiety. "One of the most important results of psycho-analytic research is this discovery that neurotic anxiety arises out of libido, that it is the product of a transformation of it, and that it is thus related to it in the same kind of way that vinegar is to wine" (1905d, note of 1920). When discussing signal anxiety, repression is no longer the origin but the consequence of the anxiety.
When an instinctual representation becomes dangerous, threatening, or guilt-ridden, it gives rise to anxiety within the ego, leading to repression. Anxiety now serves to alert the subject to the dangers associated with the possible separation and is no longer simply the expression of an instantaneous and automatic anxiety reaction to loss or separation.
See also: Anxiety.
Freud, Sigmund. (1905d). Three essays on the theory of sexuality. SE, 7: 130-243.
——. (1926d). Inhibitions, symptoms, and anxiety. SE, 20: 87-172.
Rank, Otto. (1924). The trauma of birth. Reprinted, with a new introduction by E. James Lieberman. New York: Dover Press, 1993.