Reality seems like something we should not need to explain.
There is a world around us. There are tables and trees, planets and people. We can see things, touch them, measure them and observe how they behave. Surely that is reality.
But philosophy begins by asking an awkward question:
How do we know that the world as we experience it is the world as it really is?
Once we start examining that question, reality becomes much less straightforward.
The World We Experience
Consider something as ordinary as a red apple.
You see its colour, feel its smooth surface and perhaps smell its sweetness. It seems as though these qualities simply belong to the apple.
But what actually happens?
Light reflected from the apple enters your eyes. Cells in the retina respond to particular wavelengths. Signals travel through the nervous system and are processed by the brain. Somehow, the result is your conscious experience of a bright red apple.
The apple itself does not experience redness.
Other creatures equipped with different sensory systems may experience the same object very differently. Some animals can detect ultraviolet light that humans cannot see. A dog’s experience of the world is strongly shaped by smells that barely enter ours.
This creates our first problem.
We do not experience the world directly. We experience the world through our senses and minds.
So how closely does the reality we experience resemble reality itself?
Is There a World Independent of Us?
The most intuitive answer is yes.
Mountains existed before humans saw them. Stars formed billions of years before anyone looked at the night sky. If every conscious creature disappeared tomorrow, Earth would presumably continue orbiting the Sun.
This general position is known as realism: there is a reality that exists independently of our perception of it.
Most of us live as realists without thinking about it.
But philosophers have questioned how much we can know about that independent world.
John Locke, for example, distinguished between qualities such as shape and motion and qualities such as colour, taste and smell. The latter depend partly upon the way our sensory systems respond to objects.
George Berkeley went much further.
He argued that everything we actually experience consists of perceptions and ideas. We never step outside our own experience to compare it with some completely independent material world.
Berkeley therefore questioned whether we need to assume that matter exists independently at all.
His idealism sounds strange to most modern readers, but the question behind it remains powerful:
If everything you have ever known about reality has reached you through experience, how can you know what reality is like independently of experience?
Appearance and Reality
The distinction between the world as it appears and the world as it really is runs throughout philosophy.
Plato illustrated the problem with his famous Allegory of the Cave.
Imagine people who have spent their entire lives chained inside a cave, able to see only shadows projected onto a wall. Because the shadows are all they have ever experienced, they naturally assume that the shadows are reality.
If one prisoner escaped and discovered the world outside, he would realise that what everyone had taken for reality was only an appearance produced by something deeper.
Plato used the story to make a much broader philosophical point. Perhaps the world immediately available to our senses does not reveal reality in its deepest form.
More than two thousand years later, Immanuel Kant approached the problem differently.
Kant argued that our minds are not passive windows onto reality. They actively organise experience.
We therefore know the world as it appears to beings like us, not necessarily reality exactly as it exists independently of our minds.
Kant called the world as we experience it the world of phenomena. Whatever reality may be like independently of our way of experiencing it he called the noumenal world, or things-in-themselves.
That creates a remarkable possibility.
Reality may exist independently of us while still being different from the reality we experience.
Is Reality Made of Matter?
Another question concerns what reality is ultimately made of.
One familiar answer is matter.
Ancient Greek thinkers such as Democritus proposed that everything was composed of tiny indivisible particles called atoms. Modern science has revealed a far more complicated picture, but the basic idea that physical reality underlies the world remains enormously influential.
This broadly physicalist view holds that everything that exists is ultimately physical, including ourselves.
Your body is physical. Your brain is physical. On this account, thoughts, emotions and memories somehow arise from physical processes taking place within the brain.
But consciousness makes the picture difficult.
A brain can be examined from the outside. Scientists can measure electrical activity, chemical changes and communication between neurons.
Yet your experience of seeing blue, feeling pain or remembering your childhood has another quality entirely: it is experienced from the inside.
How does subjective experience arise from physical matter?
This is one reason the question What is reality? quickly leads to another of philosophy’s great questions: What is consciousness?
Could Mind Be Fundamental?
Not every philosopher has believed that matter is the fundamental ingredient of reality.
Idealist philosophies give mind, consciousness or experience a more central role.
Berkeley argued that what we call physical objects ultimately consist of ideas perceived by minds. Later forms of idealism became considerably more complicated, but they share the suspicion that describing reality as nothing more than mind-independent matter may be incomplete.
Other positions attempt to avoid choosing between mind and matter.
Perhaps both emerge from something more fundamental. Perhaps our categories of “mental” and “physical” reflect the way humans divide up reality rather than reality’s deepest structure.
These possibilities remain controversial.
But consciousness creates an important challenge for any complete description of reality: a theory of the universe must somehow account for the fact that conscious experience exists within it.
What Has Science Revealed About Reality?
Science has transformed our picture of the world.
The apparently solid objects around us are composed of atoms. Atoms themselves contain mostly empty space, with their behaviour arising from interactions among smaller particles and fields.
Relativity showed that space and time are not the fixed universal background they appear to be in everyday life.
Quantum physics produced even stranger results.
At very small scales, particles cannot always be understood as tiny versions of familiar objects following definite paths. Quantum systems are described in terms of probabilities, and properties such as position and momentum do not behave according to everyday intuitions.
None of this means that quantum physics proves that reality is an illusion, that consciousness creates the universe or that “anything is possible”. Such claims go well beyond what the science itself establishes.
What quantum physics does show is something subtler and perhaps more interesting:
reality does not have to behave according to human common sense.
Our intuitions developed while interacting with medium-sized objects moving relatively slowly through the environment around us. There is no reason to assume those intuitions reveal the universe at its most fundamental level.
Science therefore gives us an increasingly powerful description of reality while simultaneously revealing how unlike everyday experience its deeper structure can be.
Could Reality Be a Simulation?
Modern technology has given an old philosophical problem a new form.
Could our entire experienced world be a simulation?
The idea sounds futuristic, but the underlying question is ancient. Descartes imagined that a powerful deceiver might manipulate all his experiences. Modern philosophers have imagined brains kept alive and supplied with artificial sensory information.
Films such as The Matrix simply turned the philosophical problem into a story.
If a sufficiently convincing simulation reproduced every sight, sound, memory and physical sensation, how would someone inside it discover that the world was simulated?
There is currently no established scientific evidence that our universe actually is a simulation.
Its philosophical value lies elsewhere.
The thought experiment forces us to distinguish between the reality we experience and whatever produces that experience.
That is essentially the same problem philosophers have been asking for centuries.
Is There One Reality?
There is another complication.
Human beings do not merely receive information about the world. We interpret it.
Two people can experience the same event differently. Cultures divide and describe the world in different ways. Language influences the categories we use when thinking about experience.
That does not necessarily mean that everyone literally inhabits a different physical reality.
It does mean we should distinguish between reality itself and our descriptions of reality.
A scientific theory, a philosophical argument, a religious worldview and a painting can all represent reality in very different ways. They may not all be making the same kinds of claims or using the same methods.
One of the most important habits in thinking about reality is therefore to ask:
Are we talking about reality itself, our experience of reality, or a model we have created to explain it?
Those are not necessarily the same thing.
So What Is Real?
Philosophy does not provide a single accepted answer.
Perhaps reality is fundamentally physical.
Perhaps consciousness or mind has a deeper role than physicalism allows.
Perhaps both the mental and physical are aspects of something more fundamental.
Perhaps an external world exists much as common sense suggests, while our brains construct the particular experience through which we encounter it.
Or perhaps some of our most basic categories will eventually turn out to be inadequate.
What we can say with confidence is that appearance and reality are not automatically identical.
Our senses reveal enough about the world for us to navigate it remarkably successfully, while science allows us to investigate aspects of reality far beyond the limits of ordinary perception. Philosophy asks what those discoveries mean and what assumptions lie behind our interpretations of them.
And that is where the question becomes especially interesting.
The more closely humans have examined reality, the stranger it has become.
Atoms replaced apparently solid matter. Space and time turned out not to be absolute. Quantum physics challenged familiar ideas about particles and measurement. Neuroscience revealed how extensively our brains construct our conscious experience.
Yet none of these discoveries has made the philosophical question disappear.
Instead, they have given us better ways of asking it.
Where the Question Leads
What is reality? sits near the centre of both philosophy and science because almost every other major question depends upon it.
If reality exists independently of our minds, how can we know it?
If everything we know arrives through conscious experience, what is consciousness?
If thoughts arise from physical brains, what is the relationship between mind and body?
And if the universe has a deeper structure or origin, we may eventually ask whether it has any purpose – and what our own place within it might be.
There may never be a final answer that satisfies everyone.
But learning to distinguish between the world, our experience of the world and the explanations we construct about it is already an important step.
Perhaps the best place to begin understanding reality is therefore not with an answer, but with the recognition that the world may be much richer than the version of it our everyday experience allows us to see.