When dreaming we have, as we have seen, a mental experience which closely approximates in intensity and reality to that of waking perception.

Consequently, dreams may leave behind them, for a time, vivid images which simulate the appearance of real images of memory.
Most of us, perhaps, have felt this after-effect of dreaming on our waking thoughts.

It is sometimes very hard to shake off the impression left by a vivid dream, as, for example, that a dead friend has returned to life.

During the day that follows the dream, we have at intermittent moments something like an assurance that we have seen our lost friend; and though we immediately correct the impression by reflecting that we are recalling but a dream, it tends to revive within us with a strange pertinacity.
In addition to this proximate effect of a dream in disturbing the normal process of recollection, there is reason to suppose that dreams may exert a more remote effect on our memories.

So widely different in its form is our dreaming from our waking experience, that our dreams are rarely recalled as wholes with perfect distinctness.