Interview by Richard Marshall.

'You ask whether we should want to be rational. That you ask this question here makes me think you assume that being rational amounts to doing what you have reason to do. I don't think that. There is much less of a connection between reasons and rationality than many people assume.'

'At the start of 'The Stern Review of the Economics of Climate Change' the economist Nicholas Stern announced that his work rested on ethical premises, and he would state what they were. His report drew strong criticism from some US economists, who claimed that ethical premises had no place in economics. I was incensed. I was by then a moral philosopher and not an economist, but I could not let economists propagate their own ethical views whilst pretending they were not ethical views at all.'

'First, climate change is very, very harmful, which means that a very great benefit can be obtained by controlling it. Second, in principle this great benefit could be distributed across people in all generations in such a way that none of them ends up worse off. That is to say, no sacrifice is required from anyone.'

John Broomeis Emeritus White's Professor of Moral Philosophy at the University of Oxford, Visiting Professor of Philosophy at Stanford University and Adjunct Professor at the Australian National University. He works on normativity, rationality and reasoning, and also on the ethics of climate change. He is the lead Author of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here he discusses how intention engages rationality, why we should want to be rational, why he doesn't think ethics is a branch of psychology, why economics needs ethics, equality, fairness as the good of equality, what is to be measured regarding the wellbeing of people, why climate change is very very harmful, how we should value policies inn regard to the threat, how to measure its cost, and whether 'well being' is a useful concept. This goes to the hard ground...

3:AM:What made you become a philosopher?

John Broome:I was a graduate student in Economics at MIT. I was sufficiently interested in philosophy that I took a couple of courses in philosophy while I was there. We were allowed to take courses at Harvard, and I went to Stanley Cavell's course on Wittgenstein.

I didn't understand much of it, but I was enthralled by Cavell's performance and by Wittgenstein. It seemed to me that I was watching deep thinking about the most fundamental questions going on before my eyes. From then on I wanted to be a philosopher.

To try and achieve that aim, I took a London MA in Philosophy after my PhD in Economics, but that wasn't enough to get me a job at a junior level in a Philosophy Department. I continued teaching economics for over twenty years more. Economics shares a number of concerns with moral philosophy - what does wellbeing consist in?, what is the value ofequality?, what is rationality? and so on - and I wrote mainly on topics that lie in this overlap between the disciplines. Eventually, at the instigation of John Skorupski, I was able to get a job at a senior level in the Philosophy Department at St Andrews.

3:AM:Starting with reasoning and normativity: if intentions aren’t automatically a reason to do anything then how can intentions engage our rationality like they do?

JB:How does a contract engage the law? Because the law requires you, if you've made a contract, to fulfil it; because the law requires you, if you fail to fulfil a contract, to pay compensation; and so on. These are facts about the law and particularly about how contracts figure in it.

How does an intention engage rationality? Because rationality requires you, if you intend an end, to intend whatever you believe is a necessary means to that end; because rationality requires you not to have contradictory intentions; and so on. These are facts about rationality and particularly about how intentions figure in it.

3:AM:Philosophers like Nagel and Razargued that reasons are the keys to normative thinking but you’ve argued that reasons don’t exhaust normativity haven’t you? And should we want to be rational anyway?

JB:Do you mean to ask whether I think normative thinking is concerned with other things besides reasons? Indeed I do. For example, normative thinking is concerned with what we ought to do. In fact, I'd say that 'What ought I to do?', 'What ought I to think?', 'What ought I to hope for? and 'What ought I . . .?' in general are the core normative questions. Thinking about reasons can help to answer them.

Then you ask whether we should want to be rational. That you ask this question here makes me think you assume that being rational amounts to doing what you have reason to do. I don't think that. There is much less of a connection between reasons and rationality than many people assume.

Still, the question is important anyway. (Not whether we should want to be rational - I think wants are not philosophically important - but whether we should be rational.) I think it's not necessarily the case that you should be rational. There are well-know examples, particularly from Derek Parfit, where very bad things would happen if you were rational on a particular occasion. On that occasion, it's not the case that you should be rational. But I do think you necessarily have at least a reason to be rational, though it could be defeated by stronger reasons not to be rational. I cannot prove this, however.

3:AM:Do you agree with Nagel when he says that he sees ethics as a branch of psychology? If it is how can armchair a priori reasonin about ethics get anywhere? Don’t we need Josh Knobe’s xphil crew to burn the armchair and work out the empirical experiments to generate useful data?

JB:No I don't agree with Nagel about that. One of the advances in moral philosophy since Nagel's The Possibility of Altruismis that we now routinely distinguish normative reasons from motivating reasons. Nagel explicitly declined to do that. Consequently, he did not distinguish the study of normativity from the study of motivation, which is a branch of psychology.

We now make this distinction.Ethics is a part of the study of normativity, and not a part of psychology. It could hardly be
independent of psychology,though,since it is intimately concerned with human minds.

3:AM:Economics has recently been accused ( see Amitai Etzioni in‘Evonomics’) of leading to unethical, anti-social thinking so do you think economics needs an ethical theory? If it does, which one?

JB:'Of course it does'. Economists constantly make recommendations about all sorts of things, from how the banking system should be organized to what should be done about climate change. What sort of 'should' is that? There are non-ethical 'shoulds', such as the way you should hold a golf club. But the economists' 'should' always involves balancing the conflicting interests of different people against each other. This makes it inevitably a matter for ethics. Since it is engaged in ethics, economics needs ethical theory to do its work well.

These days many economists deny this. They are so thoroughly immersed in their own ethical assumptions that they don't recognize them for what they are. The explicitly ethical branch of economics is known, oddly, as 'welfare economics'. When I was a student in economics around 1970, we were taught serious welfare economics, including such topics as the value of equality and the theory of 'optimal taxation'. But soon after that, welfare economics stopped being taught in most US universities, and a generation grew up in ignorance of it.

It was this ignorance that drew me back to work with economists ten years ago. At the start of 'The Stern Review of the Economics of Climate Change' the economist Nicholas Stern announced that his work rested on ethical premises, and he would state what they were. His report drew strong criticism from some US economists, who claimed that ethical premises had no place in economics. I was incensed. I was by then a moral philosopher and not an economist, but I could not let economists propagate their own ethical views whilst pretending they were not ethical views at all. So I found myself once again working with economists on climate change, to try and make sure they recognized their ethical premises.

3:AM:Indeed it's true that you engage in some of the most urgent ethical issues around. When discussing equalityyou have developed the idea of priority taken from economists. Can you say what this idea is and why it’s important
to thinking about equality?

JB:Many philosophers think that, in the distribution of wellbeing among people, priority should go to the worse off. Improving the wellbeing of people who have less wellbeing is more beneficial than improving the wellbeing of those who have more. This 'prioritarian' view tends to favour equality in the distribution of wellbeing. For a particular quantity of wellbeing, if it could be added to the existing wellbeing of a well-off person or else to the wellbeing of a badly-off one, the
priortarian view favours giving it to the badly-off one.

Prioritarianism appeared in economics (not under that name) at least as early as Amartya Sen's book On Economic Inequalityin 1973. The theory of it was worked out during the 1970s. It was rediscovered independently by philosophers around 1990. Philosophers could have learnt a lot by reading the extensive earlier work of economists on the value of equality, but few of them did so.

I am not myself impressed by prioritarianism. To make sense of it we have to distinguish two quantitative notions. First, we need a quantitative notion of a person's wellbeing. Then we need a separate quantitative notion of how much a person's wellbeing counts towards the general goodness of the world. I doubt we can properly construct these two different notions.

3:AM:So what is the good of equalityand given the lack of it both in many of the advanced nations as well as between the first and thirdworld what should be done? Should we level down?

JB:I think the good of equality is fairness. Fairness requires that people with equal claims to a good receive equal amounts of it. When one person is as meritorious as another, but receives less, she suffers unfairness.

This general thought leaves a lot to be filled in. What good may people have equal claims to? Is it wellbeing, or a chance of wellbeing, or a share of the Earth's resources, or something else? And what does a person's claim depend on? Is it just hard work, say, or does it depend also on some other sort of merit? I'm sorry to say I do not have worked-out views on these particular questions.

But I do agree that the existing inequality in the world is egregious. What should be done is to lessen the inequality, but I have no idea how that is to be achieved, when more and more of the political power is being cornered by the rich.

But true levelling down is never a good thing. It cannot be, because it does no one any good. Suppose the stolen wealth of an evil despot is destroyed; is that not a good thing? Yes, it probably is, but only because all the people are a little better off than they were. They are not better off in wealth but they are in fairness. The despot had much more than he deserved, which imposed unfairness on all the people. This was a harm they suffered, which has been removed. So the destruction of
the despot's wealth is not truly levelling down; it benefits the people.

3:AM:A notorious problem with measuring value (the parade case is working out the unit of value in utilitarianism) is how to measure it. How do you propose to answer this tough problem). You’ve written about the example of ‘measuring the burden of disease’ so perhaps that would be a good case to sketch.

JB:I don't propose to answer the question of how to measure value. For one particular sort of value - the wellbeing of people - I do have an answer to the question of what is to be measured. That is to say, I have an account of what a quantity of wellbeing is. How to measure it is a quite separate matter. The quantity of an electric charge is the number of
electrons over and above the number of protons, or vice versa. You measure this using an electrometer together with a calculation of capacitance; that's a quite different matter.

So what is a quantity of wellbeing? Our ordinary quantitative concept of wellbeing is very vague, so all I can do is describe a way of making it precise. There are alternative ways of doing so. The one I shall describe is useful for some purposes.

I can't explain it all in detail, but I can give you an idea of how a precise scale of wellbeing can be generated. We can do the scaling by means of uncertain chances. Compare two possibilities for a person. She could have a quality of life a for sure. Alternatively she could be exposed to an uncertain situation where she will either have a better quality of life b or else a worse one c, with an equal chance of each. Suppose these two possibilities happen to be equally good for her. Then we reckon the difference in value between a and b to be equal to the difference in value between a and c. Comparing differences in value like
this is enough to give a scale of value.

3:AM:You mentioned earlier your involvement with economists and the issue of climate change. So let's turn to that issue. What are the most important things about climate change?

JB:First, climate change is very, very harmful, which means that a very great benefit can be obtained by controlling it. Second, in principle this great benefit could be distributed across people in all generations in such a way that none of them ends up worse off. That is to say, no sacrifice is required from anyone. We have been told that the present generations must sacrifice some of its standard of living for the future. In principle no such sacrifice is required. To respond to climate change, we do not need to appeal to people's morality; we can appeal to their self-interest.

That is the position in principle. It is a consequence of some elementary economics. Greenhouse gas is a externality: the harm caused by emitting gas is not all borne by the person who emits it. When there is an externality, there is what economists call 'inefficiency'. And what they mean by that is that someone can be made better off without anyone's being made worse of. No sacrifice is required.

That is in principle. To bring it off in practice is not so easy. But the international effort should be directed towards making it possible. Appealing to the morality of governments will not work.

3:AM:How should we value policies in response to climate change?

JB:By balancing their benefits against their costs.

This doesn't mean using the methods of crude economics. Crude economics measures costs and benefits by people's willingness to pay for the benefits or be compensated for the costs. With proper correction, this can work for those benefits and costs that consist of gains or losses in human wellbeing. Correction is required because money has different values to different people: a dollar means much more to a poor person than to a rich one.

But most of us think there are benefits and harms that do not consist in human wellbeing. Climate change is very harmful to animals, for example. It is also very damaging to the inanimate natural world, and this too may be a harm that needs to be taken into account. Some economists believe their methods can capture these harms too, but they are mistaken about that.

These harms are almost certainly not precisely measurable on the same scale as human wellbeing. This means that the balance of harms and benefits is vague and indefinite. That is to be expected.

3:AM:Can the cost of global warming be measured?

JB:Climate change will affect the size of the world's population. In the extreme, it may even cause our extinction, bringing our population to an end. The hardest thing is to set a value on increasing or decreasing population, and on extinction.

3:AM:Is the notion of ‘well-being’ precise enough now to be useful? Aren’t incommensurate and immeasurable values always going to mean we’re not going to be able to agree a unified ethical solution to more or less anything?

JB:The world doesn't work by agreement. We have political processes whose whole purpose is to manage disagreement. What we have to do as philosophers is figure things out as well as we can, and present our conclusions to the world, using the best arguments we can find. That is our contribution to the political process.

3:AM:Does your overall position on ethics make you an ethical realist or an anti-realist?

JB:I'm a realist. But that is by nature rather than by argument. My book Rationality Through Reasoningis intended to show that realism is a possible, consistent view. It is not intended to demonstrate its truth.

3:AM:And for the readers here at 3:AM are there five books, other than your own, that you could recommend to take us further into your philosophical world?

JB:The five that have had a biggest effect on my life are:

JB:Wittgenstein Philosophical Investigations

Nagel The Possibility of Altruism

Parfit Reasons and Persons

Jeffrey The Logic of Decision

Bratman Intention, Plans and Practical Reason

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