Back in the day, a concatenation of circumstances led to me being alone in a room with a well-known economist who was then advising governments around the world. I thought I'd start the conversation with the anodyne remark "it must be a fascinating challenge to give policy advice in so many different places."

"No", he replied. "The same policies work everywhere."

I was surprised by this. One of us is wrong here, I thought, and if it's me, at least nobody is getting hurt.

I was reminded of this by this Venn diagram, reproduced by Tim.

The diagram's force rests upon the belief that the same policies work everywhere - that a price rise has the same effect in all markets.

But this is precisely what advocates of higher minimum wages question. One argument for them is that a higher price of labour won't reduce demand - because employers have monopsony power, or because higher wages will be offset by lower turnover.

This highlights two different ways of thinking about policy, pointed out by Edmund Burke, as discussed (pdf) by Jesse Norman.

On the one hand, he said (par 12 here), there is "the nakedness and solitude of metaphysical abstraction". The Venn diagram depends for its power upon this way of thinking - that the abstractions of Econ 101 work everywhere.

Burke, however, rejected this:

Circumstances (which with some gentlemen pass for nothing) give in reality to every political principle its distinguishing colour and discriminating effect. The circumstances are what render every civil and political scheme beneficial or noxious to mankind.

From this perspective, Krugman and other advocates of minimum wages are making a reasonable point. The circumstances of labour markets are not the same as those of carbon markets, so political schemes that are beneficial in the one can be noxious in the other.

Now, I don't say this to defend minimum wages. I think a much better way to help the low-paid would be to strengthen their bargaining power via policies such as expansionary macro policies, a serious jobs guarantee, a basic income and stronger trades unions. Instead, I do so to point out that if you wish to argue against minimum wages you must counter the monopsony-style arguments.

Snarking about inconsistency might be good enough for Oxford Union-style debating knockabout. But it's not serious economics. And- given the Burkean dichotomy - nor is it good philosophy.