What Can You Really Be Sure of When You Look at a Tomato?
When you can’t doubt the redness
You’re sitting at the kitchen table, staring at a tomato. Is it real? You could be dreaming, or stuck inside a simulation. Almost everything can be doubted. But as you look, one thing seems impossible to deny: there is something red and round right now in your awareness.
The British philosopher H.H. Price (1899–1984) made this exact point in his 1932 book Perception. He wrote, “when I see a tomato there is much that I can doubt. … but that something is red and round then and there I cannot doubt.” He called that red something a sense‑datum (plural: sense‑data). A sense‑datum is whatever you are directly aware of in a perceptual experience — the immediate colour, shape, feel — not the physical tomato itself. For Price, this flash of certainty wasn’t trivial. It was the starting point of all knowledge about the world.
How illusions blow up ordinary seeing
Price used everyday illusions to show that what your mind directly grabs isn’t the object’s surface. Place a straight stick in water and it looks bent. You experience a bent shape. But the stick itself is straight. So the bent sense‑datum cannot be the same thing as the straight stick.
A simple view, which Price called Naïve Realism, says that when you see an object, the sense‑datum is literally part of the object’s surface. The bent‑stick illusion makes that impossible — the surface of the stick isn’t bent. So we must accept that sense‑data are different from physical objects. Price argued that we simply have no choice but to admit sense‑data exist. Yet he remained metaphysically neutral: he refused to say whether sense‑data are mental, physical, or neither. The evidence from experience shows they are there, but not what ultimate stuff they are made of. That rule — don’t guess beyond what experience tells you — was typical of him.
A detective’s kit for doing philosophy
Price approached every problem with a small toolkit he never abandoned.
First, follow the evidence of experience, even if it points toward strange things. (He kept an open mind about telepathy, simply because he thought honest reports existed.)
Second, he was an empiricist. Every idea, he said, must be “cashable” by experience. To understand the concept red just is to be able to recognise red when you see it. A concept isn’t a word or a picture in your head — it’s a recognitional capacity.
Third, he defended common sense. He argued that science cannot undermine our most basic beliefs (like trusting our senses) because science itself is built on those beliefs. If you try to use science to prove your eyes are liars, you’ve already trusted your eyes to read the scientific data.
Fourth, he stayed metaphysically neutral whenever the evidence was silent. If two theories fit the same observations, he would say both are possible and refuse to pick one just to feel tidy.
This made Price a builder rather than a demolisher. He wanted to leave every problem “in a more nearly soluble state” than he found it.
From speckles to solid things: building a world
If we start with only sense‑data, how do we ever come to believe in tables, trees, and other people? Price said your mind performs perceptual acceptance. When you look out the window and see a tree, you don’t weigh evidence or make an inference. You just take it that a tree is there. It isn’t full knowledge — you could be hallucinating — but it’s a basic attitude your mind is built to take.
As you move around an object, you receive a stream of sense‑data from different angles. Your mind groups them into a “family” of sense‑data. Price thought each physical thing actually has two sides: a hidden physical occupant that does causal work (reflecting light, for instance) and a family of sense‑data that you could experience. You never see the physical occupant directly; you infer it from the sense‑data. Still, the experiences confirm each other in a rational pattern. He called this the Principle of Confirmability: your sense‑data give you good, though not absolutely certain, reason to believe in physical objects. That’s the best we can ask for.
Thinking about what isn’t there: recognition and concepts
Price later asked a deeper question: how do we ever learn to think about things at all? His answer was recognition. A genuine concept — like cat — is not a word or a mental picture. It’s a capacity to recognise cats when you encounter them. This fits his empiricism perfectly: a concept must be “cashable” by experience, otherwise it’s not really a concept.
He distinguished primary recognition (spotting a colour as red) from secondary recognition (recognising a lump of metal as lead by using its grey look as a sign). Animals do a lot of secondary recognition. A cat hears the clink of the food tin and recognises it as a sign of dinner; Price called that sign‑cognition.
This also explains how we can think about things “in their absence.” You can daydream about your cat while you’re at school because you have a recognitional capacity ready to fire. Price argued that thinking doesn’t need mental images; words and dispositions work fine. In fact, he was one of the first to carefully separate the meaning of signs (clouds mean rain) from the meaning of words (the word “rain” means rain), anticipating ideas that would later become famous.
Why a shy philosopher still matters
Price was a quiet, reclusive professor who never sought a fan club. Yet his ideas ripple through philosophy, cognitive science, and everyday life. When researchers study how babies learn to recognise faces, they echo his insight that recognition comes before language. When you put on a virtual‑reality headset, the goggles feed you artificially generated sense‑data. Can you ever be sure there isn’t a real apple behind those pixels? Price would say: start with the experience you cannot doubt, and build outward from there.
He didn’t claim to have final answers. He thought the job of a philosopher was to make problems more tractable, not to pretend we’ve solved them. That honest, patient way of thinking — follow the evidence, respect common sense, stay neutral when you must — remains a powerful model for tackling big questions.
Think about it
- If a VR headset gives you sight, sound, and touch that feel exactly like a real tomato, could you ever be certain there isn’t a real tomato in front of you? What would Price say?
- Suppose a friend has seen hundreds of photographs of tomatoes but never a real one. When you hand her a real tomato, does she instantly recognise it? What does that tell us about what concepts are?
- Price stayed neutral on many questions because the evidence didn’t settle them. In your own life, when is it smart to stay neutral like that, and when do you need to take a stand?
