Dreaming
Authors: Revonsuo Antti 
Published: February 2023

Dreaming is one of the most mysterious mental states. When we dream, we experience sensations, perceptions, actions, emotions, and thoughts while our bodies lie immobile in our beds. Our dream experiences are organised into episodes that seem to happen in real places that contain real objects and other people who are independent of ourselves. We can even communicate and interact with the other dream characters. During the dream we typically take it for granted that the events, places, and people around us are real; we are oblivious to the real state of affairs and are unable to critically evaluate it until we wake up. On waking we might feel as if we have just come back from some kind of alternative reality where we experienced adventures and dangers together with other people.
The philosopher’s task is to raise – and answer – the questions: what is the fundamental nature of the reality where we had our dream experiences? In what sense does that reality exist at all? Is dreaming a physical phenomenon, a brain state, or a purely mental phenomenon? How is the world that appears to us related to our physical world, our bodies, and the activities in the brain during sleep? These are metaphysical queries about the nature of dream phenomena. But dreams also raise epistemic worries: how is it possible that we are so totally deceived by dream experiences that we take them to be real, and furthermore we take ourselves as really being personally present in another reality while dreaming? How do we ever know for certain that we are not dreaming right now? These are epistemological worries. Both types of worries, raised by the mere existence of dreams, have been raised throughout the history of philosophy.
Recently the focus in dream philosophy has mostly been on the metaphysical questions: what is the fundamental nature of dreaming? Does the dream world consist of realistic perception, or is it akin to illusion or imagination? Where, in the physical world, is the dream world located?
The earliest metaphysical ideas about dreaming can be found in the ancient cultural, religious, and cosmological beliefs in which dreams played an important role prior to the development of Western philosophy (see §1). Similar beliefs about dreams can be found all over the world among traditional peoples. By contrast, in the history of Western philosophy, dreaming was no longer regarded as a part of a mystical cosmology, but rather was treated as a mental phenomenon that is connected to activities in our sense organs or in the body. Most philosophers argued that dreaming can literally replicate our perceptual experiences, which led to worries that if dreams can so very convincingly deceive us, we cannot know anything about the external world for certain, because everything we experience might be just a dream.
The twentieth-century ideas and developments in dream philosophy took a very different perspective of the fundamental nature of dreaming (see §2). Philosophy of mind was at that time strongly influenced by logical behaviourism. This approach aimed to get rid of mental concepts that refer to internal subjective phenomena, because such phenomena cannot be objectively observed. In the 1950s Norman Malcolm presented a conceptual analysis of dreaming in this spirit. In the 1970s Daniel Dennett continued along similar lines and proposed that a cognitive theory of dreaming need not assume that dreams are internal subjective experiences. Although empirical dream research had been enjoying a golden age since the discovery in the 1950s of REM sleep as a neurophysiological correlate of dreaming, at this time there was little interaction between philosophy and dream research.
In stark contrast to the earlier twentieth-century behaviouristic approaches, revolutionary changes in dream philosophy have taken place in the early twenty-first century (see §3 and §4). With the emergence of a science of consciousness around the turn of the millennium, philosophy, neuroscience, and cognitive science in interaction started to explore the fundamental nature and physical basis of subjective mental phenomena. Thus, dreaming and the results of dream research came into contact with the science of consciousness and the philosophy of mind, resulting in a complete turn of the tides, at least in comparison to Malcolm and Dennett’s earlier dream theories. Three philosophers of consciousness and dreaming, Antti Revonsuo, Thomas Metzinger, and Jennifer Windt have developed theories of consciousness whereby the concept of dreaming and the results of dream research play a crucial part. They all defend the idea that dreaming is a virtual reality or a realistic world-simulation constructed inside the brain. Dreaming is a form of phenomenal consciousness: there is something it feels like to have a dream. This new world-simulation concept of dreaming and consciousness has been widely accepted and adopted in empirical dream research, too, and most empirical theories of dreaming and dream function are consistent with it. Although there has been remarkable unification and progress made in the scientific and philosophical understanding of dreaming and consciousness, it is still a mystery how the neural activities in the brain can bring about a subjective phenomenal world within which we are totally immersed during both dreaming and waking perception.