The idea that there is a Book of the World containing all the world’s facts, and that science is the way to discover the contents of that book, dates back to Galileo. That belief, that reality can be exhaustively described by science, has gone hand in hand with the belief that the world contains only physical things. But as a famous 20^th century philosophy thought experiment by Frank Jackson demonstrated, some facts about the world can’t be discovered by reading books. But unlike what Jackson thought, this doesn’t show that the world isn’t physical, but that not all facts about the world can be stated by science, argues Tim Crane.

When Galileo wrote in 1623 that God had written the book of the world in squares and circles, what he meant was that the fundamental way we should understand the physical world was in terms of mathematics. The idea of a Book of the World is the idea of a book in which all truths are written down, the truths about everything that has happened and will happen, the truths about the laws of nature, the truths about our minds, about society, art, music and so on. Everything. This suggests not just a theory of the world, but also a list every truth or every fact. If there were a God, we might say, and if he is really omniscient, then the Book of the World would list all and everything he knows: all the facts.

Obviously there is no actual Book of the World in this sense. But if there could be such a book, then it might seem that someone who knew the contents of the book would know absolutely everything, all the facts. One of analytic philosophy’s most famous thought experiments —Frank Jackson’s 1982 story of Mary in the black-and-white room — suggests this idea. Jackson used this story in an argument (the ‘Knowledge Argument’) aimed to show that physicalism – the theory that claims that all facts are physical facts – is wrong. But I don’t believe the argument shows this – what it does show is that not all facts can be expressed by science, and therefore a Book of the World cannot exist.

In fact, there can be no such thing as a Book of the World. It is an impossible ideal.

The facts, the whole facts, and nothing but the facts

The idea of ‘all the facts’ is a seductive one. Some metaphysical theories of the world — the most general and abstract accounts of reality which philosophers and scientists create — use the idea with enthusiasm. Physicalism (also known as materialism), for example, says that all facts are physical (or material). Or it might say that all fundamental facts are physical, and the less than fundamental facts can be somehow derived from the fundamental ones. It seems a short step from here to say that someone who knew all the physical facts would thereby know all the facts — all truths about the world. It might look, therefore, as if physicalism is committed to the idea of a Book of the World.

But in fact, there can be no such thing as a Book of the World. It is an impossible ideal. This, I will argue, is the real lesson of Jackson’s Knowledge Argument. This argument has had thousands of pages written on it in the last forty years, and it has even appeared in mainstream fiction (in David Lodge’s 2001 novel, Thinks…). This is partly, I think, because the story is so simple, and its consequences so puzzling.

I’m sure the story is familiar to many IAI readers, but let me give a brief exposition to remind you. Imagine there is a scientist, call her Mary, who knows everything there is to know about the science of colour, colour vision and all the underlying physics (the theory of light, of matter and so on). Let’s abbreviate this by saying that she knows ‘all the physical facts’ about colour. But let’s suppose too that she has lived all her life in a black and white room, and has seen no colours other than black, white and various shades of grey.

Then one day Mary is given a ripe red tomato. She already knew tomatoes were red and she knew that she was seeing a tomato. But nonetheless, it seems that she learns something new: what red things look like. She didn’t know what red things looked like before seeing the tomato. She learns something new.

Jackson thought he could use this argument to show that physicalism — understood as the idea that all facts are physical facts — is not true. For if Mary learns a fact which she did not know before seeing the tomato, and yet she knew all the physical facts before this, then not all facts are physical facts. That is the simple consequence of the story as told. But if physicalism is defined as the doctrine that all facts are physical facts, then Jackson’s argument refutes physicalism.

It seems extraordinary however that you could refute a grand metaphysical doctrine about the entire world with a simple thought experiment and a few definitions. So what is wrong with the argument?

Not all facts are book-learning facts. Not everything you can learn comes from a book: facts about what colours look like, for example.

There have been two main responses to the argument from physicalists. One is to dispute the whole apparatus of the thought experiment: we don’t really know what we are talking about when we talk about someone knowing ‘all the physical facts’, so why should we be so certain that if someone knew all the physical facts they would not know what red looks like? The second response is to say that Mary doesn’t really learn something new, or a new fact. She might learn a new concept, or gain a new ability to recognise red, or maybe she just comes to ‘know red’ as you might know a person or a place — but none of these amount to really knowing a fact.

There is a lot that can be said about each of these responses, and their variants, but I won’t pursue these here, since it seems to me that neither response gets to the real heart of the matter. My view is that if we hang onto two simple and uncontroversial features of the Mary story, we can see how the argument does establish something interesting — but it does not refute physicalism.

Facts and truths

The first feature is that the argument is not really about the science of physics, as opposed to chemistry, biology or psychology or any other science. If the story illustrates that Mary knows all the physical facts about colour — that is, facts stated in the language of physics — then it could also add that she knows all the facts about colour which use any other scientific concepts. In fact, even if there was such a thing as a genuine science of parapsychology — which there isn’t, of course — then Mary could learn its principles too: the principles of telekinesis, telepathy and so on.

The point is that what Mary can learn in the black and white room are not just the physical facts — but any facts which do not require any experience of colour. These are the kinds of facts that Mary could learn from a (black-and-white) book. Let’s call facts like these, ‘book-learning’ facts.

The second feature is that ‘fact’ in the argument must have a particular meaning, if the argument is to make any sense. The ‘facts’ Mary learns are the truths about colour. Truths in this sense are just things you can learn. When you learn historical facts at school, what you learn (at the very least) are truths about what happened in history. Learning facts (in this sense) and learning truths are the same thing.

There is a second sense of ‘fact’, however. When Ludwig Wittgenstein wrote in his 1921 book, the Tractatus Logico-Philosophicus, that ‘the world is the totality of facts’, he didn’t think of facts as truths - the world couldn’t be made up of true claims, that makes no sense. Wittgenstein thought of facts as being in the world, not as a true claims.  Both senses of ‘fact’ are useful; we just need to be clear about which one we mean when using the word.

My point is that for the Mary story to make sense, facts must be understood as truths, not as things in the world, since truths are what we can learn. Things in the world are not what we learn — we learn things about them: that is, we learn truths about them.

But we also need to make another very important point about facts or truths. You can learn new truths about a thing (new facts, in the first sense) when you think about it in one way rather than another, without this new knowledge requiring the discovery of any new entities in the world (any new facts in the second sense). For example, when I learned that George Orwell’s original name was Eric Blair, I learned something new, a new truth about Orwell. But this did not change my view about how many entities are in the world: I did not discover the existence of an additional person. I just learned something new — a new fact, a new truth — about a person whose existence I already knew about. So just because you learn a new truth about something, that doesn’t imply that you have learned that anything new exists.

If I am right, neither the science of physics, nor any other science, could express all the truths; but the world could nonetheless be wholly physical.

The two important features of Mary’s situation, then, are (1) that what she learns in the room is a bunch of book-learning facts; and (2) that ‘facts’ here means truths. Putting these two features together, we can draw the following conclusion. Before seeing red for the first time, Mary knew all the scientific truths that she could learn from a (black-and-white) book: the book-learning truths. After seeing red, she then learned some non-book-learning truths: truths about what red looks like.

Therefore not all facts are book-learning facts. Not everything you can learn comes from a book: facts about what colours look like, for example. When Mary learns what red looks like, she can express this by pointing at something red and saying ‘this is what red looks like!’.

Of course, this does not mean that anyone who heard those words could know exactly what she meant — if she was talking on the phone to someone who had never seen red, for example, then they would not know exactly what truth she was expressing, even though they understood all of her words. But that doesn’t mean is that there is no truth about what red looks like — it just means that these truths could not be known by someone without the relevant experience.

If there are such truths, then there cannot be such a thing as a Book of the World. For the Book of the World must be something whose truths can be learned simply by anyone who understands its language, regardless of their experience. But what the Mary story shows is that even when you understand the language, there are truths that can be learned only by having certain experiences. Book-learning, no matter how comprehensive, cannot teach these truths.

Mary doesn’t refute physicalism

Where does this leave physicalism? Well, if physicalism is the doctrine that all facts are book-learning facts or truths, then physicalism really is refuted by the Mary argument. Not all facts are book-learning facts. But if I were a physicalist, I would not express my view in that way. I would say that physicalism is the view that all entities — all things in the world — are physical, but not that all truths are book-learning truths, the kind of truths that could be learned in a black-and-white physics book. If I am right, neither the science of physics, nor any other science, could express all the truths; but the world could nonetheless be wholly physical. The proper lesson of the Mary argument is that physicalists, like everyone else, should reject the idea of a Book of the World, and should not express their doctrines in terms of it. Whether physicalism, properly understood, is correct, is then another matter.