A selection from Freud's essay The Uncanny, 1919.
...the “uncanny” is that class of the terrifying which leads back to something long known to us, once very familiar. How this is possible, in what circumstances the familiar can become uncanny and frightening, I shall show in what follows.
The German word unheimlich [Throughout this paper “uncanny” is used as the English translation of “unheimlich,” literally “unhomely” —Trans.] is obviously the opposite of heimlich, heimisch, meaning “familiar,” “native,” “belonging to the home”; and we are tempted to conclude that what is “uncanny” is frightening precisely because it is not known and familiar. Naturally not everything which is new and unfamiliar is frightening, however; the relation cannot be inverted. We can only say that what is novel can easily become frightening and uncanny; some new things are frightening but not by any means all. Something has to be added to what is novel and unfamiliar to make it uncanny. On the whole, Jentsch did not get beyond this relation of the uncanny to the novel and unfamiliar. He ascribes the essential factor in the production of the feeling of uncanniness to intellectual uncertainty; so that the uncanny would always be that in which one does not know where one is, as it were. The better orientated in his environment a person is, the less readily will he get the impression of something uncanny in regard to the objects and events in it. It is not difficult to see that this definition is incomplete, and we will therefore try to proceed beyond the equation of unheimlich with unfamiliar.
In Daniel Sanders’ Wörterbuch der deutschen Sprache (1860), the following remarks [abstracted in translation] are found upon the word heimlich...
I. Also heimelich, heinielig, belonging to the house, not strange, familiar, tame, intimate, comfortable, homely, etc.
II. Concealed, kept from sight, so that others do not get to know about it, withheld from others, cf. Geheim [secret]; so also Heimlichkeit for Geheimnis [secret]. To do something heimlich, i.e. behind someone’s back; to steal away heimlich; heimlich meetings and appointments; to look on with heimlich pleasure at someone’s discomfiture; to sigh or weep heimlich; to behave heimlich, as though there was something to conceal; heimlich love, love-affair, sin; heimlich places (which good manners oblige us to conceal). [...] “‘Unheimlich’ is the name for everything that ought to have remained . . . hidden and secret and has become visible,” Schelling. “To veil the divine, to surround it with a certain Unheimlichkeit.”—Unheimlich is not often used as opposite to meaning II.
...among its different shades of meaning the word heimlich exhibits one which is identical with its opposite, unheimlich. What is heimlich thus comes to be unheimlich. [...] In general we are reminded that the word heimlich is not unambiguous, but belongs to two sets of ideas, which, without being contradictory, are yet very different: on the one hand it means what is familiar and agreeable, and on the other, what is concealed and kept out of sight [editors note: i.e., in the sense of being kept within the confines of the home, and not exposed to public view. Unheimlich is customarily used, we are told, as the contrary only of the first signification of heimlich, and not of the second. Sanders tells us nothing concerning a possible genetic connection between these two sorts of meanings. On the other hand, we notice that Schelling says something which throws quite a new light on the concept of the Unheimlich, for which we were certainly not prepared. According to him, everything is unheimlich that ought to have remained secret and hidden [i.e., in the home] but has come to light.
Thus heimlich is a word the meaning of which develops in the direction of ambivalence, until it finally coincides with its opposite, unheimlich. Unheimlich is in some way or other a sub-species of heimlich. Let us bear this discovery in mind, though we cannot yet rightly understand it, alongside of Schelling’s definition of the Unheimlich. If we go on to examine individual instances of uncanniness, these hints will become intelligible to us.
The theme of the ‘double’ has been very thoroughly treated by Otto Rank (1914). He has gone into the connections which the ‘double’ has with reflections in mirrors, with shadows, with guardian spirits, with the belief in the soul and with the fear of death; but he also lets in a flood of light on the surprising evolution of the idea. For the ‘double’ was originally an insurance against the destruction of the ego, an ‘energetic denial of the power of death,’ as Rank says; and probably the ‘immortal’ soul was the first ‘double’ of the body. This invention of doubling as a preservation against extinction has its counterpart in the language of dreams, which is fond of representing castration by a doubling or multiplication of a genital symbol. The same desire led the Ancient Egyptians to develop the art of making images of the dead in lasting materials. Such ideas, however, have sprung from the soil of unbounded self-love, from the primary narcissism which dominates the mind of the child and of primitive man. But when this stage has been surmounted, the ‘double’ reverses its aspect. From having been an assurance of immortality, it becomes the uncanny harbinger of death.
The idea of the ‘double’ does not necessarily disappear with the passing of primary narcissism, for it can receive fresh meaning from the later stages of the ego’s development. A special agency is slowly formed there, which is able to stand over against the rest of the ego, which has the function of observing and criticizing the self and of exercising a censorship within the mind, and which we become aware of as our ‘conscience.’ In the pathological case of delusions of being watched, this mental agency becomes isolated, dissociated from the ego, and discernible to the physician’s eye. The fact that an agency of this kind exists, which is able to treat the rest of the ego like an object — the fact, that is, that man is capable of self-observation — renders it possible to invest the old idea of a ‘double’ with a new meaning and to ascribe a number of things to it — above all, those things which seem to self-criticism to belong to the old surmounted narcissism of earliest times.
But it is not only this latter material, offensive as it is to the criticism of the ego, which may be incorporated in the idea of a double. There are also all the unfulfilled but possible futures to which we still like to cling in phantasy, all the strivings of the ego which adverse external circumstances have crushed, and all our suppressed acts of volition which nourish in us the illusion of Free Will. [Cf. Freud, 1901b, Chapter XII (B).]
But after having thus considered the manifest motivation of the figure of a ‘double,’ we have to admit that none of this helps us to understand the extraordinarily strong feeling of something uncanny that pervades the conception; and our knowledge of pathological mental processes enables us to add that nothing in this more superficial material could account for the urge towards defence which has caused the ego to project that material outward as something foreign to itself. When all is said and done, the quality of uncanniness can only come from the fact of the ‘double’ being a creation dating back to a very early mental stage, long since surmounted — a stage, incidentally, at which it wore a more friendly aspect. The ‘double’ has become a thing of terror, just as, after the collapse of their religion, the gods turned into demons.