What, if anything, is wrong with the Kaldor-Hicks principle? This is the question raised by Chris Whitty's argument that the benefits of reopening schools outweigh the costs of doing so.

Even if we suppose that this is factually correct - which it might not be - it does not follow that it is right to reopen schools. As David Hume said, we cannot derive "ought" from "is".

Which is where the Kaldor-Hicks principle comes in. It says that a policy change is an improvement if the beneficiaries of it could compensate the losers and still remain better off - even if compensation is not actually paid. This idea fills the Humean gap between the statements "the benefits of reopening schools exceed the costs" and "schools should reopen".

Which leads to the question I started with. I fear there are two problems with it, one philosophical, the other psychological.

The psychological problem is that it's very easy to glide from "the benefits exceed the costs" to "the benefits are high: the costs are low." Johnson might be guilty of this when he says the risk of getting Covid-19 in schools is "very small"; he forgets that a small chance of a nasty event is something to be avoided. On the Today programme this morning Tory MP Huw Merriman went further, declaring schools to be safe.

Brexit gives us another example of this. Many Leavers - especially those whose media profile is disproportionate to their cognitive skills - have gone from "the benefits of Brexit outweigh the costs" to downplaying any costs at all.

Rather than face tricky, marginal decisions we exaggerate benefits and understate costs. Psychologists call this the choice-supportive bias.

The philosophical problem arises from the fact that the winners and losers from reopening schools are different people. Children win by getting a better education, but school staff and their families lose because they face a higher risk of catching Covid-19. And even a small extra risk across tens of thousands of people adds up to a few certain deaths. How is it legitimate to impose death upon some so that others benefit, especially when they are not being compensated for that risk?

There's a long tradition which says it is not. John Rawls objected that the Kaldor-Hicks principle (which is just a refinement of classical utilitarianism) "does not take seriously the distinction between persons." And from a different perspective, Robert Nozick wrote:

There is no social entity with a good that undergoes some sacrifice for its own good. There are only individual people, different individual people, with their own individual lives. Using one of these people for the benefit of others, uses him and benefits the others. Nothing more. What happens is that something is done to him for the sake of others. Talk of an overall social good covers this up (intentionally?) To use a person in this way does not sufficiently respect and take account of the fact that he is a separate person, that his is the only life he has. He does not get some overbalancing good from his sacrifice, and no one is entitled to force this upon him. (Anarchy, State and Utopia, p32-33).

Reopening schools is, however, not the only example of the government ignoring Rawls and Nozick's objections. The awarding of A levels did the same thing. Until the government over-rode it, Ofqual graded students not just on the basis of their own abilities but on the basis of their school's past performance. As Frances says, "the algorithm did not treat people as individuals. It reduced them to points on a curve." It too did not take seriously the distinction between persons.

In truth, policy often does this. And the costs it imposes are often not just pecuniary as they are with taxes or Brexit. Fiscal austerity and benefit sanctions killed thousands of people so that the media could get the sense that the public finances were under control. And wars in Iraq and Afghanistan killed tens of thousands in the hope of benign regime change.

Such decisions are not always the result of bad policy (not that bad policy is always avoidable). Whenever a local authority decides not to reduce a speed limit it is in effect imposing a higher risk of death or injury so we can benefit from greater convenience on the roads. As Tom says, "at government level, everyone's a utilitarian."

Even in a liberal democracy, people are sometimes killed for the greater good. Rather than face this fact and think about it seriously, governments simply forget Rawls and Nozick's objections.

Which brings us to a problem. Whilst we accept this in some contexts, we rail against it in others. Here's James Bloodworth on the "useful idiots" who defend repressive regimes:

What is contemptible is the relegation of other human beings to pawns in the supposed historical process. The latter results in people uttering glib phrases about "omelettes not being possible without broken eggs" when bouts of mass killing threaten to undermine a favoured cause.

For me, Arthur Koestler's Darkness at Noon was as much an attack upon classical utilitarianism - the idea that some should suffer or die for the greater good - as it was upon Soviet communism.

There is, then, an inconsistency here. Sometimes we accept deaths for the greater good and sometimes we don't*, preferring to pretend that we cannot put a price on human life even though we often must.

This is not to accuse anybody of hypocrisy. Very few of us apply moral principles consistently (and perhaps we shouldn't). The brute fact is, though, that politics is sometimes a matter of life and death. This fact is like the first Mrs Rochester: we'd like to lock it away and forget it, but we cannot.

* I'm not sure this can be resolved merely by the fact that critics of the Soviet Union were in fact objecting to the ideal of communism rather than its implementation.