At this moment, something remarkable is happening.
You are not simply processing these words. You are aware of them.
You see shapes and colours. You may hear sounds around you. You have thoughts, memories and perhaps an emotional response to what you are reading. There is a private inner world that seems to accompany the activity of your brain.
This is consciousness.
Nothing could seem more familiar. We experience consciousness every waking moment.
Yet explaining why it exists may be one of the most difficult problems in philosophy and science.
We know that brains process information. But why should any of that processing feel like something from the inside?
And why is there an experiencing you there at all?
What Do We Mean by Consciousness?
Consciousness can mean several things.
Someone waking from anaesthesia may be described as becoming conscious. We can be conscious of a sound or a pain. We can consciously decide to concentrate on something.
But the deepest philosophical meaning is simply subjective experience.
There is something it is like to see blue.
There is something it is like to taste coffee, hear music, feel embarrassed or remember your childhood.
Philosopher Thomas Nagel famously approached the problem by asking what it is like to be a bat.
A bat experiences the world using sensory abilities very different from ours. Science can tell us a great deal about its brain and echolocation, but would possessing all those facts tell us what the bat’s experience actually feels like to the bat?
That first-person perspective is at the centre of the mystery.
The Brain and Consciousness
One thing seems increasingly clear: human consciousness is intimately connected with the brain.
Change the brain and conscious experience can change.
Alcohol alters it. Anaesthetics can apparently remove it temporarily. Brain injuries can transform perception, memory and personality. Psychedelic drugs can dramatically alter the experience of self, time and the surrounding world.
During ordinary sleep, consciousness changes and sometimes seems to disappear before returning in dreams.
Neuroscientists can increasingly identify brain activity associated with perception, attention and different states of consciousness.
So there is overwhelming reason to investigate consciousness through the brain.
But identifying the brain processes associated with an experience creates another question:
Why are those processes accompanied by experience at all?
The Hard Problem of Consciousness
The philosopher David Chalmers famously distinguished between what he called the relatively “easy problems” of consciousness and the “hard problem.”
The easy problems are not actually easy. They include understanding how the brain recognises objects, directs attention, stores information, controls behaviour and reports internal states.
These are enormously difficult scientific problems, but we can at least imagine how research might solve them.
The hard problem is different.
Why should any of this information processing produce subjective experience?
A computer can process information about wavelengths of light. A camera can distinguish colours.
But does either one see red?
When your brain processes light of a particular wavelength, you do not merely respond appropriately.
You experience redness.
Why?
That explanatory gap is the hard problem.
Could Consciousness Simply Be Brain Activity?
The most common scientific starting point is physicalism: consciousness ultimately arises from physical processes in the brain.
On this view, we do not need a separate soul or non-physical mind to explain experience. Consciousness is something the brain does.
There are good reasons for taking this seriously.
Every conscious experience we can investigate appears closely related to brain activity. Damage particular areas of the brain and particular abilities can disappear. Alter brain chemistry and experience changes.
Perhaps consciousness seems mysterious simply because neuroscience is still young.
People once did not understand life. Some believed living things required a special vital force beyond ordinary matter.
Biology eventually explained many processes of life through chemistry and physics without needing such a force.
Perhaps consciousness will follow the same path.
What seems inexplicable today may eventually become another natural phenomenon we understand.
But not everyone thinks this solves the problem.
Even a complete description of what every neuron is doing seems to describe the brain from the outside.
Consciousness is what that activity feels like from the inside.
How do we cross that gap?
The Problem of Other Minds
There is another curious fact about consciousness.
You know directly that you are conscious.
But you cannot directly experience anyone else’s consciousness.
You infer it.
Other people speak, laugh, suffer, remember and behave much as you do. They have brains broadly similar to yours. It therefore seems overwhelmingly reasonable to believe they possess inner experiences too.
But the principle becomes less obvious as we move away from humans.
Is a dog conscious?
Almost certainly in some meaningful sense.
What about an octopus?
A mouse?
A bee?
A fish?
As nervous systems become simpler and increasingly different from ours, identifying where consciousness begins becomes difficult.
There may not even be a sharp dividing line.
Perhaps consciousness exists in degrees or different forms rather than simply being switched on or off.
Could a Machine Become Conscious?
Artificial intelligence makes the question even more difficult.
A machine can process information, recognise images, use language and produce behaviour that appears increasingly intelligent.
But intelligence and consciousness are not necessarily the same thing.
A system might become extraordinarily capable without experiencing anything at all.
Imagine a machine that says:
“I am frightened. Please don’t switch me off.”
Does that prove it feels fear?
Not necessarily.
The words could simply be the output produced by its programming and information processing.
But humans also produce speech through physical processes occurring inside brains.
So what would count as evidence that an artificial system had crossed from processing information to experiencing it?
We currently have no generally accepted test for machine consciousness.
Until we understand what produces consciousness in ourselves, determining whether a very different system possesses it may remain extremely difficult.
The Philosophical Zombie
Philosophers have developed an unusual thought experiment to expose the problem.
Imagine a being physically identical to you.
Its brain contains exactly the same neurons. It laughs at jokes, avoids pain, talks about its emotions and insists that it is conscious.
But inside there is nothing.
No colours.
No pain.
No thoughts being experienced.
No inner world at all.
This hypothetical creature is called a philosophical zombie.
Nobody is suggesting that such beings actually walk among us.
The question is whether such a creature is even conceivable.
If an exact physical duplicate could behave identically without consciousness, perhaps physical facts alone do not explain subjective experience.
Physicalists generally reject the conclusion, arguing that a genuinely identical physical brain would necessarily have the same conscious states.
But the thought experiment reveals the central puzzle beautifully.
Why isn’t a human being simply an extraordinarily sophisticated biological machine operating in the dark?
Why is there experience as well?
Where Is the Self?
Consciousness also contains something else that seems obvious until we examine it:
the self.
Experience appears to happen to someone.
There seems to be a continuous me looking through my eyes, remembering my past and making decisions about my future.
But neuroscience has not discovered a tiny observer sitting somewhere inside the brain.
Different processes handle vision, memory, emotion, language, attention and decision-making.
Our apparently unified experience seems to emerge from the coordinated activity of many systems.
This raises another possibility.
Perhaps the self is not a separate thing inside the brain.
Perhaps it is something the brain constructs.
The philosopher David Hume reached a similar conclusion long before modern neuroscience. When he looked inward for a permanent self, he found only a changing stream of perceptions, thoughts and feelings.
The question then becomes even stranger:
If the self is constructed by the brain, who is experiencing the construction?
Is Consciousness in Control?
We naturally imagine consciousness as the commander of our behaviour.
A thought appears:
I’ll pick up that cup.
Then the hand moves.
It feels as though the conscious decision caused the action.
But neuroscience shows that a great deal of behaviour begins outside conscious awareness.
We recognise faces, interpret language, regulate movement and respond emotionally without consciously directing every step.
Sometimes our bodies even begin responding before we become fully aware of why.
Does that mean consciousness is merely watching decisions made elsewhere in the brain?
Probably not so simply.
Conscious thought can clearly influence behaviour. We can stop ourselves acting on an impulse, imagine future consequences, rehearse skills, reconsider beliefs and deliberately develop new habits.
Conscious processes can also affect what becomes automatic later.
Perhaps consciousness is less like a tiny pilot controlling every movement and more like a system capable of reflection, planning, correction and learning.
That possibility connects consciousness directly with the problem of free will.
Why Did Consciousness Evolve?
If consciousness arose through biological evolution, presumably it either provided some advantage or accompanied processes that did.
But what advantage does experience itself provide?
Intelligence is clearly useful.
An organism that can recognise danger, remember food locations, predict events and adjust its behaviour has obvious advantages.
But could all of those functions theoretically occur without an inner experience?
If so, why did evolution produce creatures for whom the world feels like something?
Perhaps consciousness allows information from many specialised brain systems to become available across the organism, enabling flexible decision-making.
Perhaps it helps us model ourselves and other people.
Perhaps consciousness is inseparable from sufficiently complex forms of information processing.
Or perhaps asking what consciousness is for assumes something that has not yet been established.
We do not yet have a universally accepted answer.
Could Consciousness Be Fundamental?
There is another possibility, much more speculative but philosophically important.
Perhaps consciousness does not emerge from completely non-conscious matter.
Perhaps some extremely basic form of experience is a fundamental feature of reality.
This family of ideas includes panpsychism.
Panpsychism does not normally claim that stones think or atoms have miniature human minds. Rather, it suggests that the fundamental ingredients of reality may possess primitive experiential properties from which complex consciousness can eventually develop.
The attraction is clear.
If experience exists at the fundamental level, we no longer have to explain how consciousness suddenly appears from something entirely non-conscious.
But another enormous problem appears.
How could countless tiny elements of experience combine to produce the single, unified consciousness you are experiencing now?
This is known as the combination problem.
There is currently no scientific evidence establishing panpsychism as the correct explanation of consciousness.
But its renewed philosophical interest demonstrates just how difficult the conventional problem remains.
Could Consciousness Change Our Understanding of Reality?
This is where consciousness connects back to the first Great Question: What is reality?
Our ordinary scientific picture begins with a physical universe.
Stars form. Planets appear. Chemistry becomes increasingly complex. Life evolves. Nervous systems develop. Eventually brains become sophisticated enough for consciousness to emerge.
That may be exactly what happened.
But consciousness introduces something apparently absent from the description with which we began:
experience.
The universe is no longer merely doing things.
At least in tiny regions of it, something is now experiencing what happens.
A human brain contains matter forged through cosmic history, organised by biological evolution into a form capable of looking at the night sky and wondering what the universe is.
Whether consciousness is simply an extraordinary product of matter or tells us something deeper about reality remains unknown.
We should be cautious about filling that gap with speculation.
But we should be equally cautious about pretending the gap has already been explained.
So What Is Consciousness?
We do not yet know.
It may be a biological phenomenon that neuroscience will eventually explain entirely in terms of brain activity.
It may be an emergent property that appears when information processing reaches a particular form or complexity.
Our current concepts may be inadequate, and future science may change the way we frame the problem altogether.
Or consciousness may ultimately reveal something about reality that physical descriptions alone do not capture.
These possibilities are not equally established, and some are far more speculative than others.
What we do know is that consciousness is closely dependent upon the functioning human brain, that it can be altered in systematic ways and that neuroscience is steadily revealing more about the processes associated with conscious experience.
What remains unexplained is why those processes are accompanied by an inner world.
The Most Familiar Mystery
There is a peculiar irony in studying consciousness.
Astronomers need telescopes to study distant galaxies.
Physicists build enormous machines to investigate subatomic particles.
Neuroscientists use sophisticated instruments to examine the brain.
But consciousness requires no instrument to prove that at least one example exists.
You are experiencing it now.
Indeed, consciousness is the one part of reality you encounter more directly than anything else.
Everything you have ever seen, heard, touched, learned or believed about the universe has appeared within conscious experience.
That does not mean consciousness creates the external world.
But it does mean that consciousness is the doorway through which every human attempt to understand reality must pass.
And that may be why the question is so compelling.
We are using consciousness to investigate consciousness, while that same consciousness is attempting to understand the universe that produced it.
Where the Question Leads
The mystery of consciousness opens doors in almost every direction.
Ask how consciousness arises from the brain and we return to the relationship between mind and body.
Ask whether conscious decisions influence behaviour and we encounter free will.
Ask whether our conscious experience accurately represents the world and we return to what we can know and what reality is.
Neuroscience asks which processes in the brain accompany consciousness.
Artificial intelligence raises the possibility of minds very different from our own.
Evolution asks how and why conscious organisms appeared.
And philosophy asks the question that remains after all those investigations:
Why is there something it is like to exist at all?
We may eventually discover that consciousness has a surprisingly straightforward explanation.
Or understanding it may require a profound change in our conception of the mind, matter or reality itself.
For now, consciousness remains perhaps the strangest fact we know:
somewhere in a universe of matter and energy, the universe has produced beings capable of experiencing it – and wondering why.