Are You Really Seeing What You Think You're Seeing?

Here’s a strange thing about your own eyes: when you look at a coin from an angle, it looks elliptical—sort of like a squished circle. But you know it’s round. You don’t believe it’s elliptical. Yet the way it looks doesn’t go away just because you know better. It still looks elliptical.

Now here’s the puzzle: what exactly are you seeing, then? Are you seeing the real round coin? Or are you seeing something elliptical that your brain then corrects? And if you’re seeing something elliptical that isn’t really there—what is that thing?

This is the kind of question that drove a philosopher named C. D. Broad to spend decades thinking about perception, time, free will, and whether your mind is something separate from your brain. He was a careful, methodical thinker who didn’t jump to conclusions. But he wasn’t afraid to follow an argument wherever it led—even if it led to some uncomfortable places.

The Coin Problem

Let’s start with something you’ve probably experienced yourself. You’re looking at a round dinner plate from the side. To your eyes, it looks like an oval. Not a perfect circle. But you know it’s round. So what’s happening?

According to what Broad called Naïve Realism, when you perceive something, you’re in direct contact with the real object itself. You see the actual plate. The problem is that the plate looks oval, but it’s actually round. So if you’re seeing the real plate directly, why does it look oval?

One possible answer: you’re not seeing the plate directly. Instead, you’re aware of something else—an elliptical something—that stands in between you and the plate. Broad called this intermediate thing a sensum (plural: sensa). A sensum is a private, temporary object of your awareness. It has the shape and color that the real object appears to have, even if the real object doesn’t have those properties.

So when you look at the coin from an angle, you’re directly aware of an elliptical sensum. That sensum is not the coin itself. But through it, you perceive the coin—you just do so indirectly.

This view is called Representational Realism. It says we perceive the world through representations (sensa) rather than directly.

Are You Sure You’re Not Hallucinating?

Broad had another reason for thinking we don’t perceive objects directly. Think about hallucinations. Imagine a drunk person who sees a pink rat that isn’t there. Their experience feels just like a real perception. They can describe the rat’s color, its shape, where it’s running. But there’s no real rat.

Now compare that to a normal perception of an actual pink rat. The person’s experience is subjectively identical—it feels the same from the inside. If the hallucination doesn’t involve direct contact with a real rat, why should we think the normal perception does? After all, the two experiences are internally the same. The only difference is what caused them, not what they feel like.

Broad didn’t think this argument proved that we never perceive objects directly. But he thought it made the simpler, more reasonable view that we don’t. The normal perception and the hallucination probably have the same basic structure: both involve being aware of sensa.

What’s a Sensum, Anyway?

This part gets technical, but here’s the basic idea.

Sensa aren’t physical objects. They aren’t out in the world like tables and chairs. They’re more like the immediate contents of your experience. When you see a white sheet of paper in candlelight and it looks yellowish, the yellowish thing you’re aware of is a sensum. The paper itself is white—you know that. But the yellowish patch in your field of vision is a sensum with yellowishness as one of its properties.

Broad thought sensa had properties like shape, size, and color. He didn’t think they had “secondary qualities” like hotness or coldness in the same way—those were trickier. But here’s the important point: sensa are the only things we’re directly aware of. Everything else—tables, coins, your friend’s face—we perceive indirectly, through the sensa they cause.

Some philosophers objected that this view leads to skepticism: if we only ever experience sensa, how can we be sure there’s anything else? Broad admitted this was a worry. But he thought the evidence for sensa was strong enough that we shouldn’t abandon the theory just because it has uncomfortable implications.

Can You Trust Your Own Mind?

Now let’s think about time. This might seem like a totally different topic, but it connects to the same kind of question: what’s really going on versus what seems to be going on?

You probably think of time as flowing. The present moment feels special. The past is gone. The future hasn’t arrived yet. This seems so obvious that it’s hard to imagine any other view.

But philosophers have argued about this for centuries. Broad changed his own mind about time several times.

Early in his career, he defended a view called Eternalism. According to this, past, present, and future are all equally real. The present isn’t special. The feeling that “now” is different from “then” is just a quirk of our psychology. In reality, all moments exist—we just happen to be located at one of them.

Later, Broad rejected this. He developed what’s now called the Growing Block Theory. According to this view, the past and present are real, but the future doesn’t exist yet. Reality is always growing as new moments become present and then slide into the past. The present is the newest slice of reality—the latest addition to the block.

This view captures something that seems true: the future feels open. We don’t think of it as already there, waiting for us to arrive. A future that already exists would mean your choices are already fixed—you just haven’t gotten to them yet.

But Broad eventually had problems with this view too. He worried that it still treated past events as somehow hanging around, coexisting with present ones. In his final view, he emphasized what he called absolute becoming: the constant supersession of one moment by another. Nothing coexists with anything else. Events happen, then they’re gone. The passage of time isn’t something that happens to events—it’s the most basic feature of reality itself.

Can You Really Choose?

Here’s another puzzle that bothered Broad. You probably think you have free will. When you decide whether to raise your hand or keep it down, you feel like you could have done the opposite. But is that feeling reliable?

Broad approached this by thinking about moral responsibility. If you ought to have done something, then it seems like you could have done it. So the question is: what kind of “could” is that?

Imagine a person getting addicted to a drug. At first, they could resist. They’re responsible. But as the addiction deepens, something changes. Eventually, it seems wrong to say they ought to have resisted—because they can’t anymore. But here’s the tricky part: even at the later stages, it might be true that if they had willed differently, they would have acted differently. The addiction hasn’t removed their ability to act on their will—it’s removed their ability to form a will that goes against the addiction.

So “you could have done otherwise” can’t just mean “if you had willed differently, you would have done differently.” That condition is satisfied even when you’re not free. You need something more.

Broad thought the only way to make sense of free will was to say that some actions are caused not by prior events (like brain states or desires) but directly by the agent—the person themselves, considered as a whole. This is called agent causation. The idea is that you cause your choices, not your desires or your genes or your environment.

But Broad didn’t think this idea made sense. He couldn’t see how a person (a continuing thing) could cause an event (a happening at a specific time) without something happening at that time to do the causing. The person just hangs there, doing nothing in particular, and then suddenly they cause a choice? That seems mysterious.

So Broad ended up in an uncomfortable place. He thought free will was impossible under determinism (where everything is caused by prior events) and also impossible under indeterminism (where some things happen randomly). Neither view gave him a satisfactory account. He concluded that free will probably doesn’t exist—and maybe couldn’t exist at all.

Is Your Mind Just Your Brain?

Finally, Broad asked a question that’s still hotly debated today: is consciousness something separate from the physical brain, or is it just what brains do when they get complicated enough?

Broad defended a view called Emergentism. The basic idea is this: when you arrange certain parts in the right way, new properties can emerge that aren’t present in the parts themselves. Water is wet, but hydrogen and oxygen atoms aren’t. A clock tells time, but no single gear does.

Broad thought consciousness might be like that. Mental properties—feeling pain, seeing red, being happy—emerge when nervous systems reach a certain level of complexity. These properties aren’t reducible to physical facts about neurons. You couldn’t predict what pain feels like just from knowing everything about brain chemistry.

To make this point, Broad asked us to imagine a mathematical archangel—a being with unlimited intelligence and perfect perception. This archangel could see every atom in your brain. They could predict everything your brain would do. But Broad argued that even this archangel couldn’t predict what ammonia smells like just from knowing the molecular structure of ammonia. They’d need to actually smell it themselves.

This is called the Knowledge Argument. It says there are facts about consciousness that you can’t know just by knowing all the physical facts. If that’s true, then consciousness isn’t purely physical. Something extra is going on.

But Broad didn’t go all the way to saying mind and body are completely separate substances (like Descartes thought). He thought mental properties are genuinely new features of the world that arise from physical complexity—but they’re still properties of physical things (brains). This is known as property dualism: there’s one kind of stuff (physical), but two kinds of properties (physical and mental).

The Big Picture

Here’s what Broad was really up to. He thought philosophy was about taking all the different aspects of human experience—science, morality, art, religion, your everyday sense of things—and trying to see how they fit together. He called this synopsis: looking at things together that we usually keep separate.

Most of us go through life treating our perceptions, our sense of time, our feeling of freedom, and our awareness of our own minds as separate topics. Broad thought the interesting questions come when you hold them all in view at once and notice the tensions between them. Your senses tell you the coin is elliptical. Your knowledge tells you it’s round. Your feeling of freedom says you could have raised your hand. Your reasoning about causes says everything, including your choices, might be determined. Your experience of consciousness feels like something special and separate. Science suggests it might just be neurons firing.

Broad didn’t resolve all these tensions. He wasn’t trying to. He was trying to map them clearly, honestly, and without pretending things were simpler than they are.

Appendices

Key Terms

Term	What it does in this debate
Sensum (plural: sensa)	The immediate object of awareness in perception—the elliptical patch you see when looking at a round coin from an angle
Naïve Realism	The view that we perceive physical objects directly, without any intermediaries
Representational Realism	The view that we perceive objects indirectly, through mental representations (sensa)
Eternalism	The view that past, present, and future are all equally real
Growing Block Theory	The view that past and present are real but the future doesn’t exist yet
Agent causation	The idea that a person themselves, not just their desires or brain states, can cause an action
Emergent property	A property of a whole that can’t be predicted from knowing all the properties of its parts
Property dualism	The view that there’s one kind of stuff (physical) but two kinds of properties (physical and mental)
Knowledge Argument	An argument that there are facts about consciousness you can’t know just from knowing all physical facts
Synopsis	Looking at all aspects of experience together to see how they fit—or don’t fit

Key People

C. D. Broad (1887–1971): A British philosopher who worked on perception, time, free will, and the mind-body problem. He was known for being extremely careful, fair to views he disagreed with, and willing to follow arguments to uncomfortable conclusions.
G. F. Stout (1860–1944): A philosopher and psychologist who defended an alternative account of sensations called the “adverbial analysis.” Broad respected him but disagreed with his view.

Things to Think About

If you accept that we perceive through sensa, how do you know your sensa correspond to real objects at all? Could everything you’re experiencing be a kind of dream or simulation? And how would you find out?
The Growing Block Theory says the future doesn’t exist yet. Does that mean your future choices aren’t fixed? Or could they be fixed by causes that exist now—like your genes or your environment—even if the future moments themselves don’t exist yet?
Broad thought free will was impossible. But most people feel like they have it. Could the feeling of free will be an illusion that’s useful to have? Or would realizing it’s an illusion change how you live?
If consciousness is an emergent property, what happens when a brain stops working? Does the consciousness just stop? Or could it persist in some form? What would count as evidence either way?

Where This Shows Up

Virtual reality and video games: When you put on a VR headset, you’re aware of a world that isn’t there. Are you experiencing sensa? The technology creates the equivalent of sensa—visual patches that represent a world you know isn’t physically present.
Debates about AI consciousness: When people argue about whether advanced AI could be conscious, they’re replaying Broad’s questions about emergence. Is consciousness something that just appears when a system is complex enough, or is it something special that needs a different kind of explanation?
The legal system: Courts assume people have free will—otherwise, why punish anyone for crimes? But neuroscience is increasingly showing that our choices are influenced by brain states we don’t control. The tension Broad identified is playing out in courtrooms right now.
Time travel movies: Every movie about time travel has to pick a theory of time. Back to the Future assumes the future isn’t fixed (like the Growing Block Theory). Arrival assumes everything exists at once (like Eternalism). The debates Broad had are the same ones these stories explore.