The Interpretation of Dreams by Sigmund Freud Chapter 6 Page 22

So far we have failed to see any necessity for this addition to the dream mixture. This necessity appears only when we follow closely the part played by the unconscious wish, and then seek information in the psychology of the neuroses. We thus learn that the unconscious idea, as such, is altogether incapable of entering into the foreconscious, and that it can exert an influence there only by uniting with a harmless idea already belonging to the foreconscious, to which it transfers its intensity and under which it allows itself to be concealed. This is the fact of transference which furnishes an explanation for so many surprising occurrences in the psychic life of neurotics.

The idea from the foreconscious which thus obtains an unmerited abundance of intensity may be left unchanged by the transference, or it may have forced