"Rational" is surely the key word. For appeasement breaks down when people pursue loathsome ends that are not amenable to negotiation or compromise, as with Nazi Germany or with Islamists who believe they are doing God's work in perpetrating genocide and conquest. History has shown us that far from preventing war, appeasement makes it more likely - and on terms favouring the aggressor. It was decades of appeasement, after all, that saddled us with our current crisis over Iran.

Straight after the 1979 Iranian revolution, the Carter Administration recognised the new Khomeini régime and offered to sell weapons to it. In response, the régime demanded the US hand over the Shah; and when it refused, Iran seized the US embassy and began 30 years of terrorism against the US and the West.

In 1997, Senator Joe Biden - Obama's running mate - encouraged trade and dialogue with Iran. The European Union followed suit by tripling its trade with Iran - which promptly diverted 70 per cent of the booty to its military and nuclear programmes. An Iranian spokesman explained: "We had one overt policy, which was one of negotiation and confidence building, and a covert policy, which was continuation of activities." Yes, it certainly pays to talk. The only question is: pays whom?

Sometimes, "back channel" talks to terrorists are unavoidable, as between Israel and Hamas in Gaza over the practicalities of life for the population. Intelligence agencies always need to talk to undesirables to get information.