Science can't state all the facts

The book of the world is a fantasy

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 20th 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.

Latest Releases
Join the conversation

Josh Samuel 20 January 2022

Really liked this article. Really clear, and well written. But the clarity makes it easier to disagree, and I found that I did. For what it's worth, here's why:
First, we never know anything with exact precision or with certainty. So, it's true that we can never perfectly know what it will be like to see a red tomato, without seeing it. But even after seeing one, we still only know something quite small, about what it's like to see a red tomato (just that particular tomato, in that light, at that moment etc, and even then, only if we have a pre-existing model of red and tomato - more on that later), and we might be mistaken (maybe it was an apple!).
Second, if we understood the "programme" that generates the qualia of the colour red, then I would guess that we could "know" what it would be like to see red, in much the same way that we can know what it would be like to see a green sky, or a blue tomato, even though we've never actually seen one (by combining other qualia and ideas that we have better knowledge of).
So, I find the Mary in the black and white room story unconvincing. It hinges on the fact that we don't understand qualia of colours yet, and tacitly assumes we never could. I believe we can. That said, I believe their explanation depends on understanding a programme that runs in the brain - a programee which is an abstract entity not a physical one (it is physically instantiated in the brain, but understanding it, means understanding the abstraction of the programme, not the physical instantiation). So, in a sense the story still refutes simplistic physicalism (there is more to understand than just the "fundamental" physical entities). But, in my version of what knowing about colours would mean, we could still learn about what it would be like to see red, from a book, in the black and white room. We would do so, in a similar way to how we can learn about the blue tomato, without seeing it, through conjectures from related qualia and ideas. In my imaginary Mary story, we would be doing it with fewer direct experiences of qualia to draw on, but with a much deeper understanding of what these qualia actually are. 

So, I accept the author's assertion that the crux of the seeming paradox, in the Mary story, lies in the idea that there are indeed no more physical entities for Mary to discover, rather she has abstract entities to discover. But I don't follow the author's contention that there are no more "book learned facts" for Mary to discover. This is a version of an empiricist view that certain truths are not book learned and can only be gained by experience. Confusingly, it's these truths based on experience that the author considers to be outside the scope of science (empiricists tend to consider truths "based on experience" to be scientific). This difference arises because the author is emphasising the need for direct personal experience to know what red looks like. But actually, I still see this as the classic empiricist error: Imagining that the rest of us "know what red looks like", because we've experienced it. No. We know what red looks like, because we have an inbuilt, evolved programme that makes conjectures about how best to group certain colours as "red", and experience merely helps us to refine that. Similarly, Mary in her room, if she fully understood colour qualia, could make such a conjecture. She would no doubt benefit from experience to refine her understanding, but the core of the knowledge could come from a book (despite the premise of the thought experiment, knowledge from a book, could never be perfect (hence the potential to refine and error correct it with experience), but that's only because no knowledge is perfect).

Eric Johnson 20 January 2022

There is one serious point of contention in the discussion about Mary and the color red. The premise assumes the color red is a fact. In reality, the color red is a perception in the brain and not a physical property. The physical properties are the spectrum of light from the source, the spectral response of the object (the apple's surface) and the sensitivity of the detecting elements in the eye. Two situations arise from this. First is the assumption Mary can see the color red. She may see that color for the first time, but it is not what everyone else would perceive since perception is unique to the observer. And different spectral interactions between a light source, an object and an observer can produce the same color perception. The physical facts are completely different but the human perception is identical and that's how paint colors are matched to a sample swatch. The physical facts are all different but in accordance to Mary's complete understanding of color appearance would know they produce the same perception.

The second point is that we live in a world where we can measure and quantify facts that have no human perception. We can measure orders of magnitude more spectrum than we can perceive with our eyes and much of our daily living is directly impacted by this. Facts can and do exist outside of the realm of direct human perception.

But this then gets deeper into this premise of perception. Is human experience a proper fact? If the complete neurological mechanism of the brain were thoroughly understood, we would see that experiences are merely biochemical responses and chemical developments in tissue and cells that may be non-quantifiable today but not in the future. As frightening as it sounds, we are really just biochemical processors that may well be scrutinized into quantifiable facts and, even more frighteningly, programmable and adjustable beyond the normal experience of natural perception and response. In such a scenario, then we, our human existence, everything we experience and our very essence, are also part of that book of facts. But just in chapters we have not read...yet.

Elrick 18 January 2022

Good article. The recent LHC announcement that looks like promoting the addition of a 5th force in this universe of ours certainly backs the the idea that there is no absolute 'Book of the World'. And like Mary being brought up in a black and white room most folk in our world are brought up with no or very little experience of stuff like telepathy/telekinesis/dowsing and so on. In my opinion and experience these are real and science ought to spend time on such things to add to a more real Book of the World!!!