Ard: We’re going to switch topics. That was great. That was really helpful.

David: Reductionism?

Ard: So why don’t you ask about reductionism because that’s the one you’re… So we’re interested in emergence and reductionism.

David: We’ve gone around asking everyone about the two and trying to get them to define both.

GE: And you’ve got 150 different answers.

David: You said it George. So would you like to add one more?

David: And I should stress, we’re not trying to be in any way anti-reductionistic. We’re just saying, what are they? What are its strengths? What are its weaknesses? Is it the answer to everything or not?

GE: Reductionism is the question: can you, in principle, completely explain what happens at the higher levels in terms of what’s happening at the lower levels?

David: And what do you think?

GE: Well my answer is absolutely not.

David: Why?

GE: I think a very good place to start is digital computers because digital computers are something which we can actually understand fully. Now a digital computer, it’s made up of all of these gates, transistors joined together by wires and then put together with a keyboard and a display and so on, and you can look at it at the different levels. At the bottom-most level it’s electrons flowing through the gates in a particular way, and that’s what controls what happens at the screens.

But given that hardware – there’s the hardware sitting there – it doesn’t do a thing until you load it up with a program, and what the identical hardware does is completely different depending on the software you load. So if you put in a word processing program, a music program, a paint program or something, you have completely different outcomes from the identical hardware. So the hardware, per se, does not determine what happens. What determines it is the program you load in. So now the question is, what is the ontological nature of a digital computer program?

David: When you say ontological…?

GE: What kind of existence does it represent? And now the hard-line reductionist will say that it’s nothing but electron states in these gates. Now that is completely wrong, and a useful side-step here is to think about what is the ontological nature of a book.

Now in the old days we all thought of a book as paper with printing on it and covers, and that’s a book. Now the question is, is it the same book if it’s got a different size print? Is it now still the same book? Is it the same book if you print it in italics or not? And I think we all agree it’s the same book. It’s different instantiations of the same book.

Nowadays we know that the book can be given to you in electronic form. Is the electronic form still the same book? And my answer is yes. The book is the abstract quantity which can be instantiated in those different ways. Now a computer program is the same: it’s an abstract entity; it’s not a physical thing. And so some people say, ‘But it’s here: it’s the CD disc.’ But it’s not the CD disc. Is it the excited states in the gates? That’s an instantiation of the computer program. And actually a computer has got layers of structure: there’s the machine language, the assembly language, there’s the operating system language, there’s the high-level language, and what is the key thing here is that there’s a logic in the computer program.

That abstract logic then gets written into a high-level code. What happens in the computer is absolute magic. The high-level code gets typed in and then interpreters or compliers write it down in to the lower-level languages.

Exactly the same logic is present at every level, but it’s represented in a different way with different rules, and at the bottom level it gets turned into instructions at the gate, and it gets turned into electronic states in the gates. Now, what is the computer program? It’s the equivalent class of all of these representations: it’s an abstract thing. Does it have causal power? Yes, it causes things to happen.

And very, very similar to this is the rules of chess and the rules of football. Those are abstract agreements and they can change with time. Now, the rules of chess determine what happens on the chess board, and I like to imagine this Martian coming and watching chess – after a while he works out these different motions, and then he picks up the rook and he looks underneath it. ‘Is something causing it?’ And then he can’t figure that out, and so he invents a force field which acts on rooks and only enables them to move in different force fields…

David: Looking for a physical explanation?

GE: Looking for a physical explanation. It’s a mental explanation. It’s a set of rules, abstract rules, and again they’re abstract, they’re not physical things. And they can be realised in a computer program or in your mind, or they can be realised in a book and so on. And again this multiple realisation, whenever you’ve got multiple realisation of some concept, it’s telling you that there’s causation from the concept to all of these realisations.

David: So you’re saying an abstract logic has this power?

GE: An abstract logic has physical outcomes in the real world through being what is implemented in a computer. So then, of course, the old philosophers of mind would say, ‘but you’re talking a dualist position.’ My answer is, ‘yes I am.’ A computer is a dualist machine: there’s the hardware and the software.

David: So you’re saying there’s a difference between the mind and its ideas, and the brain?

GE: Yes, I take the completely unpopular position: I’m a dualist. There’s the mind and the brain, and the mind inhabits the brain… or thoughts, thoughts inhabit the brain and thoughts are not physical things. Thoughts are abstract things which get represented in a physical way.

And again we do not understand how this happened, but the brain has a hierarchical structure. Thoughts have a hierarchical structure, and in the computer you can see these different levels. You can understand them, and you have got these interpreters or compilers which do it. I think eventually when we understand the brain enough, we will see exactly the same kind of structure happening in the brain.

The logic is going top-down from the top level down to the bottom and it is the logic which is controlling what happens at the bottom level. Abstract entities are driving the physics at the bottom level. The physics is not controlling what happens.

David: So that is exactly the opposite of when people say the reductionistic picture is always once you’ve understood these things at the bottom, they are what cause things to happen?

GE: Yep.

David: The cause always runs from the bottom up?

GE: Well it goes both ways, and there’s a large literature on what is called supervenience.

David: What is supervenience?

GE: Supervenience is if I knew everything about the bottom-level state – and let’s take the computer as an example – so I know the wiring and the chip; if I knew at an instant all of the states of the electronic gate, and then I reproduced it over there in another computer in exactly the same way, then it would give you exactly the same high-level stuff there. So at that level the reductionist picture is correct.

But the question is, how did those bottom-level states get to be in the excitation states that they are? And that can only happen top-down from the logic controlling what happens at the bottom level. And something similar like that will be happening in the mind.

David: I was just thinking about why so many scientists are really wedded to reductionism, and is it because they think the only thing that you could add into the universe, that isn’t what the reductionist story has in it, matter, that they think you’re going to import the supernatural? Whereas you’re importing something that is not supernatural. You’re saying there’s a realm of ideas, which isn’t supernatural.

GE: No, it’s not supernatural in that sense. The ideas don’t reach down and act of themselves.

David: No.

Ard: Like ghosts.

David: No, true, okay.