s might disagree about whether the results are robust or whether the controls are adequate, and they might suggest additional experiments, there is rarely fundamental disagreement about what sorts of experiments are relevant to the hypothesis. It’s not so with: ‘We are interested in whether the brain computes.’ This naturally suggests… what? There’s not been wide agreement about what experiments one should run to test this general hypothesis or even about what phenomena this general hypothesis is supposed to explain. While the statement ‘the-brain-computes-X’, treated as a chunk, might be a perfectly good, well-understood scientific hypothesis, it will take a lot of work to say exactly what the crucial part of the sentence ‘The brain computes…’ says all by itself.
The claim that the brain is a computer is not merely a metaphor – but it is not quite a concrete hypothesis. It is a theoretical framework that guides fruitful research. The claim offers to us the general formula ‘The brain computes X’ as a key to understanding certain aspects of our astonishing mental capacities. By filling in the X, we get mathematically precise, testable and, in a number of cases, highly supported hypotheses about how certain mental capacities work. So, the defining claim of the theoretical framework, that the brain computes, is almost certainly true.
Though we are in a position to say that it is likely true that the brain is a computer, we do not yet have any settled idea of what it means for the brain to be a computer. Like a metaphor, it really is unclear what the literal message of the claim is. But, unlike a metaphor, the claim is intended to be a true one, and we do seek to uncover its literal message.
Even if you agree to the literal claim that the brain computes since, after all, our best theories hold that it computes X, Y and Z, you might be unsure or disagree about what it is for something to be a computer. In fact, it looks like a lot of people disagree about the meaning of something that they all agree is true. The points of disagreement do not spoil the point of agreement. You can have a compelling reason to say that a claim is true even before you light upon a clear understanding of what that claim means about the world.
Often, we get our hooks into some general phenomenon and hold on for dear science
This position isn’t so uncommon in science. The concept of temperature could be put to good scientific service even before we had any real conception of what it was – a conception that was developed through a lot of labour and ingenuity. In the early 1960s, the American physicist Richard Feynman said that it ‘is important to realise that in physics today, we have no knowledge of what energy is’, and it’s debated how much better off we are now. And while Albert Einstein offered a detailed theory of gravity, we don’t have a full-enough understanding of what gravity is to reconcile it with the other fundamental forces. See also: quantum mechanics (I won’t say any more than that because I don’t know any more). Scientific hypotheses have often yielded good predictions and insightful explanations, often by applying mathematical principles to natural systems, even though, when it comes to saying what it really means for the world to be as the hypothesis says… that takes some figuring-out.
Throughout the history of science, we have often started by knowing just enough to be able to point to an important thing, though we didn’t grok it well enough to paint the full picture. We do not need to start with a fixed, fully fleshed-out conception of some deep feature of the world and then see whether it fits our observations. Often, we get our hooks into some general phenomenon as we try to solve specific problems, and we have to drag ourselves closer and closer to the phenomenon underlying those problems, developing our understanding over the course of generations, sometimes withstanding fierce swings and great setbacks as we hold on for dear science. We’re on to something when we say the brain is a computer, but it might not be clear for a whi