Pope Benedict XVI's visit to Britain to beatify John Henry Newman neatly coincided with the threat of a 75 per cent cut in government support for arts and humanities teaching. The Cardinal is only one or two miracles away from sainthood, but the thought that a prayer to the author of The Idea of a University might result in more intelligent government policy and Newman's final step to sainthood is hard to entertain. On the other hand, it's not clear what else can save us.

One difficulty is that the defenders of liberal education - essentially education aiming at producing enlightenment rather than the ability to fix computers, get clients off drink-driving charges or mend broken limbs - are never sure what terrain to fight the philistines on. Defending an education based on Matthew Arnold's "the best that has been thought and said in the world" against those who want more plumbers, those who believe against all the evidence that a focus on STEM (science, technology, engineering and mathematics) subjects will create a second Industrial Revolution, and those who just don't see the point of educating the lower orders in the first place is no easier now than when he wrote Culture and Anarchy almost 150 years ago.

There are three different arguments that most people defending the arts and humanities will run; they are not at odds with each other, but none is completely plausible, even when not vulnerable to the snort of disbelief that would greet anyone appealing to Newman's claim that the object of a university is to produce "gentlemen". Nor does it help the arts and humanities that the best arguments favour what the Americans call "the liberal arts and sciences" rather than the arts and humanities in particular.

The first line of defence is to deny the opposition between "vocational" and "non-vocational" education. Knowing a lot about Plato isn't as immediately useful as knowing a lot about cash flow if you want to run a leisure centre, but the person who knows a lot about Plato will be a very quick study; the Treasury was better at managing the country's affairs when its recruits had mostly read Classics than it is today. But when money is tight, it's hard to resist the thought that saving money on liberal education and spending it on directly vocational education is common sense.

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The second line of defence is that liberal education is a bulwark of a democratic culture and essential to the creation of a democratic citizenry. This view has been defended with some passion by Martha Nussbaum in Not for Profit: Why Democracy Needs the Humanities. But it's not obvious that anything resembling liberal education is either necessary or sufficient to produce democratic citizens and a democratic culture. Many highly educated people have been profoundly anti-democratic; even if one effect of a passion for philosophy or literature is to make one wish that everyone could share that passion, it's not obvious that it leads in any particular political direction.

There is some evidence that more educated people are more tolerant than the less educated, but it is patchy. The trouble with anything difficult - whether philosophy or mountaineering - is that it swiftly sorts out the best from the merely competent and them in turn from the incompetent, while the essence of democracy is that citizens have a say because they are citizens, not because they are good at something. What sustains a democratic culture is hard to say, but it must include fellow-feeling for those with whom we share our political system, and the knowledge that unless our rulers answer to the rest of us, they will look after their own interests. Untutored good nature and common sense seem more likely to sustain democratic politics than any amount of education.

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The third line of defence is that besides knowing how to make things and do things, we need to know why to make and do whatever it is. As Socrates observed, the doctor who could make a herbal decoction that would restore your health could also brew a poison that would put an end to you. Techniques can be used by the vicious as well as the virtuous. Liberal education allows us to reflect on the point of human existence, and to make wise decisions about what to do with our technical skills. You don't need to take a Luddite view of technological progress to think that our capacity for producing new things, whether physical (like cars and aeroplanes) or immaterial (like derivatives), is more impressive than our ability to obtain their benefits without suffering too many drawbacks.

Once again, it's not very plausible that we make a mess of things because we are short of moral insight. We usually make a mess of things because we do not know what the side-effects of what we do will be, or because we have built institutions that allow those who benefit from whatever it may be to dump the hazards on everyone else, or because we make irrational decisions for the reasons so elegantly explored over the past two decades by psychologists such as Daniel Kahneman. Few people believe that pollution is a good thing, or that bankruptcy and homelessness fall only on those who deserve what they suffer. Societies like that of the UK or the US display a high degree of consensus on moral values, but a lot less on the consequences of any particular policy.

Surprisingly, the best defence comes from Arnold himself, who expected the cultivated mind to allow a "stream of fresh and free thought" to enliven our stock opinions. That, if anything, is the benefit both to individuals and society at large; and it suggests that humanities, social sciences, and physical sciences are all in the same boat - taught well, they liberate us; taught badly, they induce mental cramp. Whether our masters understand any of that, heaven only knows.