The ability to have control and consciousness in the dream state, also known as lucid dreaming. According to Hereward Carrington (in his book Higher Psychical Development, 1924) dreamers can keep conscious control up to the moment of falling asleep. He advises:
"When you have learned to do that, then construct before yourself, mentally, a definite scene, which you must hold firmly in mind. Then, as you are falling to sleep hold this scene before you, and at the very last moment, before you fall asleep, consciously transfer yourself into the scene—in other words, step into the picture; and if you have developed yourself to the requisite point, you will be enabled to carry over an unbroken consciousness into the dream state; and in this way you have a perfect continuity of thought; there is no break in the consciousness; you step into the dream picture and go on dreaming consciously. That is the process of dreaming true, and after this dream is fully enacted, then you should remember perfectly all that has transpired during the sleep period."
In the book The Projection of the Astral Body by Sylvan J. Muldoon and Carrington (1929), Muldoon remarks that these instructions are in harmony with the method of dream control used to induce the astral body to move out into space. An article in the Proceedings of the Society for Psychical Research (vol. 26, July 1913) records van Eeden's experiments in dreaming true. The British psychical researcher J. Arthur Hill vouches for the truthfulness of the experiences in The Dreams of Orlow (1916), by A. M. Irvine.
Muldoon, Sylvan J., and Hereward Carrington. The Projection of the Astral Body. London: Rider, 1929.