Some skeptics of lucid dreaming suggest that it is not a state of sleep, but of brief wakefulness, or 'micro-awakening'. Experiments by Stephen LaBerge used 'perception of the outside world' as a criterion for wakefulness while studying lucid dreamers, and their sleep state was corroborated with physiological measurements. Nonetheless, LaBerge admits the criterion is subjective.
Others point out that there is no way to prove the truth of lucid dreaming other than to ask the dreamer. According to Dr. Patrick McNamara of Boston University, there is no scientific way to know for certain that someone is dreaming other than to wake them up and ask them. Meanwhile, Professor Norman Malcolm say that the only criterion of the truth of a statement that someone has had a certain dream is the dreamer saying so. Malcolm further describes lucid dreaming as absurd and impossible, recalling as an example, "I dreamt that I realised I was dreaming, dreamt that I was affecting the course of my dream, and then dreamt that I woke myself up by telling myself to wake up."
Philosopher Norman Malcolm argued against the possibility of checking the accuracy of dream reports, pointing out that 'the only criterion of the truth of a statement that someone has had a certain dream is, essentially, his saying so'.