In February 1944, Winston Churchill held a luncheon party at Number 10. His wife, Clementine, was there, as was his secretary, Jock Colville, plus a few selected guests, including Irving Berlin, the songwriter. 

Some weeks earlier, Churchill had received a briefing note from one of the staff at the British Embassy in Washington. He was so impressed with it that he asked who the writer was. ‘Isaiah Berlin’ came the reply. The note’s powerful quality stuck in Churchill’s mind and when Clementine told him that Irving Berlin was staying in London, he insisted that he should come to lunch.

During the meal Churchill asked Irving Berlin about the likelihood of President Roosevelt being re-elected. Berlin replied that he thought the chances were very high and added: “But if he won’t stand again, I don’t think I’ll vote at all.”

Churchill was slightly puzzled. He then asked Berlin when he thought the war would end, and Berlin said: “I shall tell my children and grandchildren that Winston Churchill asked me that question…”

Becoming even more puzzled, Churchill asked him: “What is the most important thing you have written?” And, to his astonishment, received the reply White Christmas… 

Sensing social disaster, Clementine brought the meal to an end, and only when everyone had gone did she explain what had happened. The man who had written the briefing note was Isaiah Berlin, but by mistake, the invitation to lunch had been sent to Irving Berlin, the songwriter.

Isaiah Berlin was a remarkable Oxford philosopher who studied the history of ideas. One of his own ideas concerns the difficulties which arise when two moral goods clash. He called it ‘incommensurabilty’: by which he meant that there are some situations where one thing that is good clashes with another which is equally good. Any decision made must necessarily sacrifice one good for another.

The problem about immigration with which politicians are wrestling is a perfect example of ‘incommensurability’. It is right that we should welcome to our country those people who have arrived legally and are fleeing for their lives, but it is also right that we should not overstretch the tolerance and capacity of our own society by doing so.

This is not just an interesting academic problem. In the real world, elected politicians must come to a judgment. Whatever they decide, as Isaiah Berlin argued, the result cannot be satisfactory. Therein lies the human tragedy.