Most of us think of ourselves either as a citizen of a nation, or a follower of a religion, or both. In many older societies, identity is shaped by family, or tribe.
Even within nations, there are cultural divisions, such as the Walloons and the Flemish in Belgium, or the Ossetians and the Abkhazians in Georgia. Within religions there are Catholic, Protestant, Greek Orthodox and other sects in Christianity and Shia and Sunni within Islam.
In the United States, it is still quite common to have people and neighbourhoods described as Italian-American, Irish-American, Cuban-American and so on. There are fewer tribal, ethnic and cultural identities in more unitary nations, such as Poland and Italy.
These sociological reflections are of little importance on a day-to-day basis, unless one kind of discrimination, or another, occurs, or unless ongoing sectarian conflicts perpetuate themselves over centuries, as in the Middle East.
Identity becomes a political issue, as for example in Northern Ireland, when a region, or province, is located in one geographical area and its sovereignty is aligned with another.
History and politics often drive these circumstances. Much turmoil in the Middle East arises from arbitrary lines on a map drawn by dominant colonial powers, France and Britain, during and following the First World War.
As an American who has studied in England and travelled in Ireland and who most recently has attempted to provide constructive support to political leaders in Northern Ireland, I have occasionally received instructions from one or more members of the local public to go home and stay home and not interfere.
But we all know there are many Americans, Irish Catholic and Scots-Irish Protestant, who care about Northern Ireland, its people and its future and who wish to help.
Among American politicians, including former politicians, my personal inclination is very much against imposing, instructing, or lecturing, other people and other nations. This is somewhat unusual in a nation some of whose politicians think America was created to direct the rest of the world in the path we most favour.
But intensive involvement in Northern Ireland politics has increasingly brought me back to this reflection: finding a common identity might hold a key to Northern Ireland's future.
The US contribution here is limited. We can continue to demonstrate concern, seek involvement in discussions, propose ideas and urge compromise. But we cannot solve Northern Ireland's problems. We can help with public contributions, exchange programs and private investments. But large-scale private investment requires a greater degree of economic and political stability.
I began adult life as a student of religion and theology and it was my religious convictions that brought me into public service as a way to better the lives of people in this life and on this earth. And it is those studies and those convictions that shape these reflections about identity in Northern Ireland and America:
In one of Plato's Dialogues, I have found my political touchstone: politics is "the art of caring for souls".
As time goes on, other Americans will come here seeking to help, as a number of distinguished Americans have done in the past. I am simply the current holder of this honour. We don't give up easily. But we also do not seek to impose ourselves on the good people of Northern Ireland.
My late colleague Daniel Patrick Moynihan said, on the occasion of John Kennedy's death, that "life will always break your heart". That may be so. But life also offers us all the chance to be better and to do better and to keep on struggling toward our shared identity. Adding to that shared identity is our common concern for our children and for their future.
We will get there if we always keep in mind that we are all human beings and we are all the children of God. That is the most important identity we share.