Nationality is a strange thing. Modern technologies, economic systems and much of our culture are international as never before. Yet as national barriers have been lowered, the sentiment of nationality has often increased. Leopold Bloom’s sublimely rational definition of a nation as ‘the same people living in the same place’ sounds even less adequate today than it would have done eighty years ago.

The main merit of Bloom’s definition, appropriately enough for a modern Ulysses, lies in calling attention to the fact that most of the problems of nationality are caused by people wandering about. For example, the trial of the other Joyce – William Joyce, Lord Haw-Haw – demonstrated that a man born in Brooklyn and brought up in Ireland could be hanged as a British traitor for war crimes committed in Germany. William Joyce and James Joyce had their British passports in common. At least James’s literary nationality has never been in doubt, though this is scarcely true of his friend and compatriot Samuel Beckett. It would be interesting to know how many British university libraries shelve Beckett’s books under French, not Irish, literature.

Traitors sell their nationality, whereas writers, if they are well-known, find themselves trading on their nationality whether they like it or not. Neither traitors nor imaginative writers can ever fully discard what we choose to call their country, though other people can, and frequently do. Who, for instance, is the greatest Irish scientist of the 20th century? The answer I would give to this conversation-stopping question is Professor J.D. Bernal FRS. Bernal, by origin a Munster Catholic, has not yet been reclaimed (so far as I know) by his country’s intellectual historians. Yet if any comparably famous expatriate novelist had been born in County Tipperary in 1901 we should have certainly heard of it.

Bernal’s decision to make his career in England was nothing extraordinary. A promising young crystallographer might take the same decision just as easily today. The political rhetoric (whether Nationalist or Loyalist) according to which London and Dublin are conceived as ‘foreign powers’ is doubtless diplomatically correct. But I would guess that the recent Anglo-Irish agreement was so eagerly welcomed in Britain because it seemed to suggest that, politically, the two countries could return to what in cultural terms they had never lost – a state of neo-colonial intimacy.