Conscious experiences of change, from seeing a bird take flight to listening to a melody, cannot be broken down into ever smaller units of experience. They must inhabit what William James called the “specious present,” a sliding window of time where the immediate past and present overlap. Philosopher Lyu Zhou argues that this exposes a deep rift between mind and matter. When the physical world undergoes change, it does so through succession – one physical state replaces another, and the past is gone – whereas consciousness requires the active retention of the past inside the present, revealing its fundamentally non-physical nature.

1. Consciousness, change and time

You are now conscious as you read this article. Is your consciousness physical? Many today think it is. They claim that it either is a physical system made of matter – most likely the neural network of your brain – or is realized by matter through a physical process, most likely by your brain through a neural biochemical process. However, I hope to convince you that this view is wrong. I hope to show you that your immediate present consciousness has certain features that physical systems and processes cannot have.

What is so novel about my argument? The most often cited reason for denying that consciousness is physical is the so-called Hard Problem of Consciousness. The Hard Problem is that it is deeply mysterious how the physical process in your brain can give rise to subjective experiences with qualities such as what it is like to see red or smell the malodor of a long-rotten potato. The apparently intractable nature of this problem suggests that consciousness is likely not physical. But the problem I want to raise today is a different and novel one. Unlike the Hard Problem, which focuses on the qualitative aspect of consciousness, my argument highlights a certain structural feature of your immediate present consciousness that nothing physical could have: it is holistic. Let me explain.

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Your immediate present consciousness is an extended whole: it is not like a snapshot, but like a short movie.

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No doubt you are currently experiencing some change, e.g. objects moving from one place to another. But what it is for there to be a change is simply for there to be different states at different times. Therefore, if you experience change at all, as you indeed do, you must experience there being different states at different times. The experience involved cannot be like a snapshot: it cannot be restricted to a mere instant. Rather, the experience must be like a short movie with a brief duration: it must have a temporal span so as to encompass different states at different times.

The snapshot conception of your immediate present consciousness faces at least one other serious problem. You seem to have a stream of consciousness in which various states come and pass away in time. These states appear before, after, or at the same time as one another along a temporal dimension that is very much like a continuous extended line. It is not without reason that it is often spoken of as a timeline. However, the sum of any number of zeros must remain zero. Likewise, the addition of any number of durationless instants—snapshot experiences—cannot give you any continuous extended timeline.

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The issue is that it is difficult to put together anything like a continuous stream of consciousness if what you have is nothing but a sum of snapshot experiences. It is indeed true that if you look at photo snapshots of a moving object in quick succession, you will experience a continuous change rather than a jumpy series of discrete static states. This is a famous optical illusion known as the color-phi phenomenon, which movies utilize. However, your experience in this case is no longer a snapshot, even though it is the photo snapshots perceived in quick succession that give rise to the illusion. Rather, the illusory experience of yours has a temporal span in which the perceived object appears in different states and hence appears as changing continuously.

Therefore, your immediate present consciousness is an extended whole: it is not like a snapshot, but like a short movie. In a famous passage, the 19^th-century American philosopher William James characterizes our immediate present consciousness as having

no knife-edge, but a saddle-back, with a certain breadth of its own on which we sit perched […] The unit of composition of our perception of time is a duration […] It is only as parts of this duration-block that the relation of succession of one end to the other is perceived. We do not first feel one end and then feel the other after it, and from the perception of the succession infer an interval of time between, but we seem to feel the interval of time as a whole, with its two ends embedded in it.

Just as your perceptual experience has an extended visual field, which is the background against which you perceive objects in space, your consciousness also has an extended temporal field, which is the background against which you experience change. Your conscious experience comes in such temporal chunks. They are the basic units of your temporal consciousness. Each unit, albeit extended, is given to you all at once.

2. The holism of conscious experience

What matters for my purpose is that there is no more basic unit of your temporal consciousness than this temporal field of yours. There is indeed a sense in which this temporal field of yours has shorter durations as its parts. But these parts are mere conceptual abstractions and are therefore derivative from the whole. You can conceive of one of them only if you start with the basic unit, divide it further in thought, and then abstract the part you want from the whole. Strictly speaking, you never experience this part by itself. It is embedded within the bigger temporal field. Like an archaeologist unearthing buried fossils or ancient artefacts, you need to start with the whole and then dig out the part you want.

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No physical process is holistic in the way your immediate present consciousness is.

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Hence your immediate present consciousness is in an important sense holistic. Its parts cannot be conceived to exist except derivatively by abstracting from the whole. This is so even if your imaginative and cognitive capacities are maximally enhanced. No such enhancement should deprive you of your experience of change. Nor should your conscious experience cease to feature a continuous extended timeline. But in order to experience change and have your stream of consciousness conditioned by a continuous extended timeline, your immediate present consciousness cannot be like a snapshot. Hence your immediate present consciousness must essentially remain an extended unit. The act of conceiving of any smaller part of it must essentially remain a process of abstraction from it as an extended whole. Therefore, even ideally, these parts cannot be conceived to exist except derivatively by abstracting from the whole. This I take to be very strong evidence that they cannot really exist on their own but merely derivatively as parts of the whole. In other words, they must depend on the whole for their existence. Your immediate present consciousness is in this sense holistic. The whole of it comes before the parts.

3. Nothing physical is holistic

No physical system is holistic in this way. What is physical does not have this special property of the whole coming before the parts or the parts depending on the whole for their existence. Take the neural network of your brain, for instance. The whole network depends on the constituent microphysical particles, which include numerous molecules, atoms, etc. It is possible to break the neural network down into smaller parts. Doing so will destroy the network but not necessarily the parts. Unlike the parts of your immediate present consciousness, these physical parts are not mere abstractions but can exist on their own even when the whole ceases to exist. This is true of any physical system. You can likewise break down a stone, a tree, a car, or a brain into smaller chunks of matter or even fundamental particles. The wholes will cease to exist, but the parts into which they are broken can still continue to exist on their own. Therefore, no physical system is holistic in the way your immediate present consciousness is. Because of this structural discrepancy, your immediate present consciousness cannot be a physical system.

But can it be a physical process? I think not. No physical process is holistic in the way your immediate present consciousness is. Consider, for instance, any neural biochemical process in your brain. Suppose that the process has begun but has not reached its end. But the world could have ended right after this instant. If the world were to end when the process is merely half-completed, then there would be a part of this process – the completed half – that exists on its own without being part of the whole process. The whole thus has a part that does not depend on the whole for its existence. This means that the whole neural biochemical process is not holistic in the way your immediate present consciousness is. In fact, this is true of any physical process in spacetime. The world could have ended when any physical process is only halfway completed, rendering that process non-holistic. Hence your immediate present consciousness cannot be a physical process either.

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Given their structural discrepancy, a non-holistic system or process cannot realize a holistic unit of consciousness. Otherwise the novel structural feature of holism would have to arise out of thin air. But this is hardly possible. Therefore, most plausibly, your immediate present consciousness cannot be physical, period.

If consciousness is not physical, what is it? On my view there are two possibilities. Unfortunately I do not know which one is true. One possibility is that it is fundamental. At the bottom level of reality, there is consciousness. There is no further explanation for it in terms of other even more fundamental entities. It itself is already fundamental. If you want to know what it is, turn inside yourself and feel it. It is your oldest acquaintance, since you are ever conscious.

The other possibility is that consciousness is not fundamental but is grounded in something more fundamental. I must confess that I have no idea what this more fundamental entity could be. But whatever it is, it cannot be physical. Can anyone ever know what it is—and not just what it is not? I am skeptical. We cannot empirically observe it. We only have access to its effects—our consciousness. Perhaps here lies the ultimate limit of human knowledge. Perhaps here we should be silent out of intellectual humility.