When an idea to be rejected has once failed to become conscious because it has succumbed to repression, it can be repressed on other occasions only because it has been withdrawn from conscious perception on other grounds.
 Sigmund Freud, The Interpretation of Dreams (1899). copy citation

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Author Sigmund Freud
Source The Interpretation of Dreams
Topic perception repression
Date 1899
Language English
Reference
Note Translated by A. A. Brill
Weblink http://www.bartleby.com/285/7.html

Context

“We learn that the repression which, though originally expedient, terminates nevertheless in a harmful rejection of inhibition and of psychic domination, is so much more easily accomplished with reminiscences than with perceptions, because in the former there is no increase in occupation through the excitement of the psychic sensory organs. When an idea to be rejected has once failed to become conscious because it has succumbed to repression, it can be repressed on other occasions only because it has been withdrawn from conscious perception on other grounds. These are hints employed by therapy in order to bring about a retrogression of accomplished repressions. 163 The value of the over-occupation which is produced by the regulating influence of the Cons.” source