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154 been recently experienced; 2. That the dream stimulus shall remain a psychologically valuable train of thought. In a single case (a) both conditions are fulfilled by the same impression. If it be added that the same indifferent impressions which are used for the dream, as long as they are recent, lose this availability as soon as they become a day (or at most several days) older, the assumption must be made that the very freshness of an impression gives it a certain psychological value for dream formation, which is somewhat equivalent to the value of emotionally accentuated memories or trains of thought. We shall be able to see the basis of this value of recent impressions for dream formation only with the help of certain psychological considerations which will appear later.

Incidentally our attention is called to the fact that important changes in the material comprised by our ideas and our memory may be brought about unconsciously and at night. The injunction that one should sleep for a night upon any affair before making a final decision about it is obviously fully justified. But we see that at this point we have proceeded from the psychology of dreaming to that of sleep, a step for which there will often be occasion.

Now there arises an objection threatening to invalidate the conclusions we have just reached. If indifferent impressions can get into the dream only in case they are recent, how does it happen that we find also in the dream content elements from earlier periods in our lives, which at the time when they were recent possessed, as Strümpell expresses it, no psychic value, which, therefore, ought to have been forgotten long ago, and which, therefore, are neither fresh nor psychologically significant?

This objection can be fully met if we rely upon the results furnished by psychoanalysis of neurotics. The solution is as follows: The process of displacement which substitutes indifferent material for that having psychic significance (for dreaming as well as for thinking) has already taken place in those earlier periods of life, and has since become fixed in the memory. Those elements which were originally indifferent are in fact no longer so, since they have acquired the value of