The subjective sensory stimuli as a source of the dream have the obvious advantage that unlike the objective stimuli they are independent of external accidents. They are, so to speak, at the disposal of the explanation as often as it needs them. They are, however, in so far inferior to the objective sensory stimuli that the role of dream inciter, which observation and experiment have proven for the latter, can be verified in their case only with difficulty or not at all.
