In the days following the end of World War II, I read that the Allied soldiers were under orders not to fraternise with the German civilians. Faced with the plight of millions of people displaced and in poverty, the Allies quickly became friends with their former enemies – it is hard to hate people you truly know.

I remember being at an Open University summer school back in the 1980s. A lecturer, late on a Thursday afternoon was trying to teach us something about sociology (or was it social psychology? No matter) . He talked about something called ‘group closure thesis’. It was near the end of the week, and I probably misunderstood what he was saying, but in my memory, he seemed to say that people could find an identity in a group by defining themselves against someone else.

I remember being slightly depressed at the idea, which I would have given more attention if it had not been for the fact that I knew I was heading to the south of France for three weeks when summer school finished the following afternoon.

Since that time, I have often wondered whether a dislike of others is a necessary part of who we are: do I need to dislike someone because they do not belong to the same group as me?

Group closure seems to carry with it dangerous baggage. Does it imply: I am (of a particular group) therefore I hate?

All of us would be able to quickly call up examples of group closure. I heard a funny story of a man from Cork coming out of Twickenham delighted because England had been beaten by France. The man is asked by a BBC reporter, would he support any team, whoever they were, against England. The Corkman said he would.

‘Well’, says the BBC man, ‘can you think of any circumstances at all where you would support England?’

The Corkman scratched his head and said, ‘Well, I suppose if they were playing Tipperary’.

I have plentiful memories of group closure by the English. I remember being told by an English woman deep in the heart of France that most of the French could speak perfectly good English and that they just didn’t want to. I hesitated to ask her why they should.

Group closure arises from fear and suspicion; the unknown worries us. When the unknown becomes known, most times the fear disappears.

Prejudice mostly arises from group closure. People are different from our group, so we dislike, even hate them. I remember listening to someone attack gay people, ‘do you know any gay people?’ I asked. Of course, he didn’t – we fear what we don’t know.

Group closure is at its strongest in gatherings like football matches, where opposing groups of mostly working class, mostly younger men, are clearly identified. The gatherings are characterised by verbal, if not physical, violence.

I was walking down a street in north Dublin a couple of weeks ago, wearing the colours of the club I supported, along with friends. A supporter of the opposition standing beside his car said it was good to see us. It was not the reception we might have expected.

Our side got hammered and we were leaving early. The same man stepped from the crowd and said he was sorry to have seen our side playing so poorly. Next time we play that team, along with the abuse we get from their supporters, I will remember the man who met us with friendship.

One individual can undermine a whole group closure.