Does reality contain only physical things? Or could everything be conscious, as panpsychists claim? Philosopher Christian List argues it’s time to move beyond both sides of this debate. Consciousness reveals something far more radical: reality cannot be captured by a single, objective description. Dualists, panpsychists and materialists all assume that there’s one unified reality that science and philosophy can aim to describe. But the deep subjectivity of consciousness shows this can’t be right. Reality cannot be contained in a single book – only a whole library of perspectives will do.

Science has been hugely successful at explaining many phenomena, from the motion of the planets to the functioning of biological organisms. But despite advances in neuroscience, explaining how consciousness fits into the world remains elusive. Why do some organisms have experiences, feelings, subjective perceptions, and so on? The hallmark of consciousness is that there is something it is like to be a conscious subject, for that subject, as Thomas Nagel famously puts it. What makes some entities conscious, and others not, and how is consciousness related to the rest of the physical world? Even worse, there is no agreement on what would count as a good answer.

The big challenge of explaining consciousness stems from the fact that consciousness is inherently first-personal: something experienced only from a first-person perspective. Ordinary science, by contrast, is entirely third-personal. This point is widely appreciated, but its ramifications for our scientific worldview are more radical than commonly recognized. My claim is that, to capture what is special about consciousness, we must accept that there are genuinely first-personal facts, over and above the third-personal facts that ordinary science recognizes.

David Chalmers distinguishes between the “easy” and the “hard” problems of consciousness. The “easy problems” are to explain the cognitive and behavioural functions related to consciousness and to figure out which brain processes underpin them. Examples of such functions are the difference between wakefulness and sleep, and the ability to respond to perceptual stimuli. These problems are “easy,” insofar as they can be approached using ordinary scientific methods. For example, scientists can use behavioural and verbal responses as external markers of consciousness and correlate these with other observable data, including data from brain scans and physiology. However, even if neuroscience will ultimately tell us which patterns of brain activity are associated with which cognitive functions, this leaves unanswered a more fundamental question: why are there conscious experiences at all? Why do certain physical processes in the brain and body give rise to subjective experiences? Why don’t these processes take place “in the dark,” without anyone having any experiences, just as the planets revolve around the sun without the solar system experiencing anything? Answering these questions is the “hard” problem. What makes it hard is that the thing to be explained, subjective experience, is first-personal, while ordinary science offers only third-personal explanations.

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None of the physical and behavioural markers of consciousness that scientists study get to the heart of what consciousness is.

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The hard problem can be illustrated by introducing the thought experiment of a “philosophical zombie.” This is a hypothetical being that displays all the physical and behavioural markers of consciousness without actually experiencing anything. No external observation, experiment, or brain scan could identify the difference between a zombie and a conscious being like you and me. The zombie looks like you and me, displays the same physical processes in the brain and body, and gives the same verbal responses. It is third-personally indistinguishable from you and me. From an observer’s perspective – even with the best scientific equipment – one can never strictly rule out the possibility that another organism is a zombie.

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Of course, no-one reasonably thinks that there are zombies in the real world. However, the thought experiment seems coherent. Though it’s science fiction, it involves no logical contradiction. What this thought experiment shows, arguably, is that none of the physical and behavioural markers of consciousness that scientists study get to the heart of what consciousness is. The consciousness that you and I have goes beyond the kinds of third-personally observable properties that science normally refers to. This has led some, including Chalmers, to take seriously the idea that to accommodate consciousness in a scientific worldview, we must postulate the existence of special kinds of “phenomenal” properties, over and above the ordinary physical properties recognized by science.

On Chalmers’s picture, incorporating consciousness into a scientific worldview would require the kind of theoretical innovation that James Clerk Maxwell and others made when they first postulated the existence of electromagnetic fields. What Maxwell showed was that the inventory of properties that exist in the physical world was richer than previously recognized. There are not only the properties related to gravity and motion, as described by Isaac Newton, but also electromagnetic properties that were missing from earlier physical theories. Similarly, Chalmers has suggested, we must recognize that the world contains not only physical properties, but also some additional “phenomenal” properties, and these are responsible for conscious experiences. It is the existence of those non-physical phenomenal properties that makes the difference between the actual world, in which there is consciousness, and the hypothetical “zombie world,” in which everything is physically the same, but consciousness is missing. Chalmers’s position, developed in detail in an influential 1996 book, is a modernized, “naturalistic” version of dualism. (Dualism of the more traditional sort, according to which the mind is a non-physical substance, distinct from the brain, is usually associated with René Descartes in the seventeenth century.)

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Despite the disagreements between physicalists, dualists and others, practically all sides in this debate share one common assumption. This is the assumption that there is a unified objective world, which science and philosophy seek to describe and explain and in which all relevant properties can be found.

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Against the dualists, physicalists such as Daniel Dennett deny that we must postulate any special phenomenal properties to account for consciousness. Our inability to explain how physical processes in the brain and body give rise to conscious experiences, they say, is due to the fact that neuroscience is insufficiently advanced. Our current inability to explain consciousness is like the inability of some nineteenth-century scientists to explain the phenomenon of life. Those scientists thought that one needed to postulate some special “vital spirit” to explain life, whereas we now know that this is unnecessary. Ordinary chemistry and biology suffice. Similarly, the reasoning goes, we will eventually understand how consciousness arises from physics, chemistry and biology alone, without having to throw any additional “phenomenal” properties into the mix.

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Much of the contemporary philosophical debate about consciousness revolves around the question just discussed: is consciousness ultimately explicable in terms of physical properties alone, or do we need something non-physical too? Might we even have to suppose that everything in our universe has both a physical aspect and a phenomenal one, as suggested by some versions of panpsychism?

However, despite the disagreements between physicalists, dualists and others, practically all sides in this debate share one common assumption. This is the assumption that there is a unified objective world, which science and philosophy seek to describe and explain and in which all relevant properties can be found. The disagreements are just about the precise inventory of that world. What exactly does that world contain? For example, are there only physical properties or also phenomenal ones? Given the heated nature of the debate, it is easy to miss the fact that there is nonetheless this shared assumption of an objective world.

What is the significance of this? It is that the conventional scientific and philosophical theories, including those dualist theories that were especially devised to account for consciousness (such as Chalmers’s), ultimately give us a third-personal picture of the world. They seek to describe and explain the world as it would be seen by an omniscient, or at least highly informed, outside observer: someone who is taking what Thomas Nagel has called “the view from nowhere.”

The attempt to abstract away from any particular perspective is a central feature of modern science. By looking beyond the particularities of specific objects, events and perspectives, science has been able to uncover general patterns and regularities: ones that are “invariant” under shifts in perspective and that qualify as candidates for general laws of nature. The history of science illustrates the move towards greater abstraction. Over time, humans went from an anthropocentric to a geocentric to a heliocentric and eventually to a more universal view of the world, and each step constituted scientific progress.

Yet the crux is that there is at least one important phenomenon that resists such objectivization or “de-perspectivization,” and that is consciousness itself. If we accept that the core of consciousness is subjective experience, then consciousness is the ultimately subjective phenomenon. The core of my consciousness lies in the fact that I find myself in a world in which there are first-personal facts. I am conscious, I have certain experiences, I am in a particular perceptual state, and so on. First-personal facts are irreducibly subjective. They are “centred” around my perspective as an experiencing subject, and unlike objective facts, they are not invariant under shifts in perspective.

Crucially, each of us is inextricably tied to our own conscious perspective. I can reflect about your experiences and empathize with you; I can hypothetically try to place myself in your shoes; I can try to simulate in my mind what things must be like for you. But I cannot literally leave my own conscious perspective. It is an essential fact about me that I experience the world from my perspective and not from anyone else’s. To be conscious, one might say, is to have a subjective perspective around which some first-personal facts are centred.

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A number of philosophers – myself included – have argued that unless we recognize the existence of such first-personal facts, we cannot adequately describe and explain the phenomenon of conscious experience. For the phenomenologists in the tradition of Edmund Husserl, the first-person perspective was the starting point of any enquiry. Without that perspective, our worldview would be incomplete. Among contemporary philosophers, Dan Zahavi, for instance, writes: “[S]ubjectivity is a built-in feature of experiential life. Experiential episodes are neither unconscious, nor anonymous, rather they necessarily come with first-personal givenness or perspectival ownership.” And Lynne Rudder Baker writes that the scientific worldview “takes the world to be impersonal; what exists are all individuals and all their properties, but none of these requires appeal to anything expressible in the first person.” And she asks how such an impersonal world could “accommodate me.” Her answer is that, to accommodate a subject’s perspective, we must recognize that “there are irreducible first-person facts.”

Similarly, Thomas Nagel argues that a purely third-personal view of the world leaves out the fact that each of us is who we are. It gives us a “description of all [of the world’s] physical contents and their states, activities, and attributes” and “a description of all the persons in the world and their histories, memories, thoughts, sensations, perceptions, intentions.” But even when the world has been fully described like this, he notes, “there seems to remain one fact which has not been expressed, and that is the fact that I am Thomas Nagel.”

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If we cannot adequately explain consciousness without postulating irreducibly first-personal facts, there simply is no single objective book of the world.

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To see the ramifications of these points, it is helpful to introduce the metaphor of the “book of the world.” This is a hypothetical massive book that contains a complete enumeration of all the facts that obtain in the world. It exhaustively describes everything that is the case in the world, up to the most minute detail, as it would be seen by an omniscient observer. According to the standard worldview in science and philosophy, as Theodore Sider summarizes it, “[t]here is an objectively correct way to ‘write the book of the world’.” It might be hard to figure out what it is, but the goal of science and philosophy is to write that book. Now, everyone understands that the complete book of the world can never be written in finite time and that we will only ever approximate part of it. But as a theoretical goal, it is widely assumed that there is in principle an objectively correct way to write that book.

However, if we cannot adequately explain consciousness without postulating irreducibly first-personal facts, there simply is no single objective book of the world. As it is conventionally characterized, that book is written from a third-person perspective. Its narrator is an Olympian observer describing the world from the outside. Such a book would fail to include any first-personal facts. It would be incomplete. So, it wouldn’t be the book of the world. For example, it would describe Christian and his experiences in third-personal terms, just as it would describe everyone else’s experiences in third-personal terms, but it would leave out the first-personal fact that I am having Christian’s experiences rather than anyone else’s. A complete inventory of reality, which includes subjective facts, could not be given in the form of a unified objective book.

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The attempt to “objectivize” consciousness – to represent it as an ordinary property that can be found in the objective world, like gravity and electromagnetism – fails to do justice to the irreducibly subjective nature of the phenomenon.

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Rather, it would require an entire library, consisting of one subjective book for each conscious subject. Each such book wouldn’t be written by an Olympian third-personal narrator, but it would reflect the first-person perspective of the relevant subject. My book of the world, which might be titled “The world as I found it” (as Ludwig Wittgenstein once proposed), would be different from yours, since it would be centred around my perspective, while your book would be centred around yours. To be sure, different such books would have some chapters in common, namely those that cover only objective facts – those that are invariant under shifts in perspective – such as the ordinary physical facts. But the different books would come apart in their subjective content. They could not be coherently merged into a single book because such a merged book could not be narrated from a unified perspective. (I assume that any potential book of the world must be coherent.)

The lesson, I think, is that the attempt to “objectivize” consciousness – to represent it as an ordinary property that can be found in the objective world, like gravity and electromagnetism – fails to do justice to the irreducibly subjective nature of the phenomenon. Physicalist theories of consciousness are not alone in running into that problem; standard versions of dualism face the same problem too. We will better understand consciousness only if our scientific and philosophical theories fully come to terms with the existence of first-personal facts and recognize that reality may not be captured by a single objective book of the world, but only by a library of subjective ones.

Author’s note: This article draws on two published papers of mine (here and here), where I have defended a “many-worlds theory” of consciousness and where more detailed literature references can be found. Fellow travellers in the exploration of first-personal facts, in addition to those mentioned above, include Kit Fine, Caspar Hare, Benj Hellie, Giovanni Merlo, Martin Lipman, and David Builes. Earlier critics of the assumption that there is a unique objective world include Nelson Goodman, Gabriel Vacariu, Ted Honderich, and Marcus Gabriel. I am very grateful to Daniel Stoljar and Laura Valentini for helpful feedback and to Philip Pettit for suggesting the “library” metaphor.