This psychoanalytic concept was coined by Sandor Ferenczi in his paper “Introjection and Transference” (1909) as the antithesis to “projection”. He defined it as taking into the ego parts of the outside world and making them the object of unconscious phantasies. Freud developed Ferenczi's idea, notably in his essay “Instincts and their Vicissitudes” (1915) and in “Mourning and Melancholia” (1917), as a contrasting dyad with his earlier term projection (first used in 1896), such that introjection becomes the process of taking into ourselves that which is associated with pleasure, whilst projection is a defensive mechanism for ejecting from ourselves …
Clark, Robert. "Introjection". The Literary Encyclopedia. First published 22 October 2005; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=564, accessed 25 April 2015.]