Internecine arguments inside the cabinet are common enough. But in failing to agree on the extent of a smoking ban, ministers can at least claim this in their defence: they are grappling with a real philosophical dilemma. Where does your right to smoke stop and my right not to breathe your smoke begin?

We can dismiss, for starters, the much touted idea that smokers represent a "minority" who are being discriminated against. Unlike, say, being black or white, smoking is a voluntary activity, not an unchosen identity. And anyway, where's the discrimination? If smoking were banned everywhere, everyone would have exactly the same degree of freedom to smoke: none.

But the question of rights is trickier. "The only purpose for which power can be rightly exercised over any member of a civilised community, against his will, is to prevent harm to others," wrote John Stuart Mill. If you agree with that, then, says Simon Blackburn, professor of philosophy at Cambridge University, "the state isn't permitted to act paternalistically, to stop you rock climbing or smoking or drinking for your own good."

So the question becomes one of harm. What constitutes being hurt by someone else's smoking? The irritation factor probably isn't sufficient: "If finding something offensive counts as harm, then your freedom of action is held hostage to any old opinion," says Blackburn, who personally welcomes a ban. Of course, passive smoking is more than irritating: government studies have shown that it increases the risk of health damage. But a pro-smoker could object that this argument is statistical - an increased chance of harm is not definite harm. That arguably makes smoking more like driving a car (you might harm others, but it's legal) than stoving someone's head in with an axe (you will harm others, and it's illegal).

The only people for whom the harm seems rather more certain are pub and restaurant workers, and it's their rights that provide the strongest argument for a ban. Meanwhile, if you buy Mill's argument, you really ought to start lobbying for the legalisation of crack and heroin, too ...