Every country has a head of state. Until 1918, only two of Europe's score of states (or several score if the German empire's 25 states of that period are counted separately) were not monarchies - France and Switzerland, writes Garret FitzGerald
And after the collapse of Europe's three empires in that year, most of the 30 states that emerged out of that conflagration remained constitutional monarchies.
Moreover, seven of Europe's pre-enlargement 15 EU member states have hereditary monarchs as their heads of state.
During the 60 years since the end of the second World War, only Greece has dethroned its monarch.
Everywhere else, despite the anomalous nature of a monarchy in a modern world, the peoples of countries where hereditary monarchy survived two world wars have been content to retain this system, albeit in some cases making succession to the throne gender-neutral.
The anachronism of hereditary succession to the headship of a state is in these countries outweighed in most people's minds by a combination of a sense of historical continuity and a lack of enthusiasm for what is generally seen as the alternative - a president elected by politicians.
In some countries an even more powerful consideration supports the retention of the monarchy. This is true, for example, of Belgium, a deeply-divided country where the monarchy is almost the only unifying factor.
It is also true of Monaco, which the dynasty protects from a merger with France, and of Spain, where the king has played a key role in re-establishing and maintaining democracy in the post-Franco era.
Where monarchs disappeared they were universally replaced by presidents - in western Europe most of them elected by political assemblies. Those bodies have tended to choose elderly politicians, people who by virtue of their past career in that controversial profession may not find it easy to become a focus for national unity.
Almost all of these presidents have a largely non-executive role - France under its Fifth Republic being something of an exception.
However, most European heads of state, be they monarchs or presidents, retain some role in proposing to parliament the name of a new head of government or, in Belgium and the Netherlands, in at least nominating someone to facilitate this process.
What is interesting about all this has been the survival, not only in Europe but everywhere else as well, of the concept of a country requiring a head of state.
The need to have some unifying figure, standing above and beyond the holder of executive office who leads the government, is almost universally seen as valuable. In this sense a vestige of the monarchical concept survives.
We in Ireland are unusual, although not unique, in that the people elect to that office rather than the Oireachtas. (The only other western European countries which follow this practice are, I believe, Austria, Portugal, Finland and Iceland).
After a good start in 1938, when an election was avoided when political unanimity was found in favour of the uncontested nomination of a non-political candidate Dr Douglas Hyde, subsequent elections were contested between candidates of the two main political parties.
But just over 30 years ago, after the tragic death in office of Erskine Childers, the parties agreed on the nomination first of Cearbhaill Ó Dalaigh, and, after his resignation, of Paddy Hillery, who, although a former Fianna Fáil Minister, was seen as someone who could transcend party politics.
This relative depoliticisation of the office, albeit at the expense of depriving the electorate of any say in the matter by way of an election, was followed by politically-contested elections which were won by candidates who had not been prominent in party politics.
Thus we have moved, partly by chance, to a relatively non-party-political presidency.
We have had a succession of heads of state who, like the surviving constitutional monarchs, have commanded widespread respect, and have been able to act as unifying figures.
There are, however, two unusual features of the Irish presidency.
First of all, unlike most other heads of state in Europe, the President of Ireland has no role in nominating the political leader whose name is put to parliament for approval.
Historically, in Europe prime ministers first emerged as appointed agents of the monarch in running a state.
Then, with the growth of the power of democratic parliaments, heads of government gradually became responsible to that institution rather than to the monarch, who generally retains the prerogative of proposing a name to parliament.
From the outset the Irish Free State Constitution provided that our head of government would be appointed on the nomination of Dáil Éireann and not of the king, as was then the case in the UK and elsewhere in the Commonwealth.
Perhaps because the president elected under the 1937 Constitution had no international recognition until the king was replaced in 1949, this has remained the situation ever since even though this lacuna creates a risk of deadlock when the Dáil resumes after an election, something that was a real possibility after I resigned following the defeat of my government in 1987.
Yet if for historic reasons our president is unusual in having no role in the nomination of the head of government for approval by the Dáil, he or she has an important power to refuse to sign legislation which, in the president's view, having heard the opinions of members of the Council of State, might be unconstitutional.
On 22 occasions since 1940 presidents have sought the views of the Council of State on new legislation. They have referred legislation to the Supreme Court 15 times, and on seven occasions part or all of a referred Bill has been struck down by the court.
In introducing this presidential power, Éamon de Valera may have been influenced by the fact that, although the 1922 Constitution had stated that "the judicial power of the High Court" (subject to appeal to the Supreme Court), "shall extend to the question of the validity of any law having regard to the provisions of the Constitution", in fact very few such appeals had been launched.
So he cannot have foreseen the remarkable growth of such individual constitutional challenges under the 1937 Constitution.
In making provision for this presidential power de Valera was conscious of the risk to human rights that existed in the UK arising from the absolute sovereignty of its parliament. His introduction into our system of this important constitutional provision reflected a concern lest the Oireachtas might at some point be tempted to exceed its powers.
He thus saw the presidency as a potential safeguard against the possibility of parliamentary tyranny or, more probably, simple parliamentary insensitivity to some human rights.