A: "Does everybody dream?" is a more complex question than it might at first appear, and a correct answer requires addressing several related questions: What is a dream? Why do we forget them? Can we really know anything about other people's minds? Let's take these one at a time.

Whether awake or asleep, the brain constructs a model of reality-consciousness from the best available sources of information. During waking, those sources are external sensory input in combination with internal contextual and motivational information. During sleep, little external information is available, so consciousness is constructed from internal sources. These include expectations derived from past experience, and motivations-wishes, such as S. Freud observed, but also fears. The resulting experiences are what we call dreams. In these terms, dreaming is perception free from external sensory constraint, while perception is dreaming constrained by sensory input-hallucinations that happen to be true.

People who have never remembered a dream are likely to do so if awakened abruptly from rapid eye movement (REM) sleep. But why should dreams be so hard to remember? Evolution is a likely factor, as explicit recall of certain dreams might well have fatal consequences. Suppose someone dreamed that a deadly toadstool was not really poisonous if consumed under the full moon. If the person later remembered this as fact the person would not be likely to live long enough to pass on genes for remembering dreams! Whatever function dreaming serves, it cannot be anything that requires the explicit recall of dreams.

"Does everybody dream?" is a variation on the philosophical "Problem of Other Minds": how can we be sure that other people have experiences of any kind at all? Skeptical solipsists will imagine that only they, and no others, have consciousness. Radical behaviorists will claim that neither they nor any other humans have consciousness.

Between these two extremes is another position: people and animals with bodies and nervous systems that are closely similar as viewed from the outside would most probably appear analogously similar if viewed from the inside. Indeed, the present writer believes that "everybody dreams" applies not just to normal adult humans but to all normal mammals. He thinks it far more likely that children, cats, dogs, whales, and bats all experience something during REM sleep, rather than that they just twitch while adult humans dream. What does he think they dream? What else but what it's like to be a child, cat, dog, whale, or bat.

Stephen LaBerge

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