The short answer is a qualified “yes” but to explain why, we must first define our terms. It is a sad truth that words often mean something different in Northern Ireland than they do elsewhere, but then clarity of thought is often the first casualty of any ideological conflict.
Compare the use of the terms “nationalist” and “republican” in the Northern Ireland conflict with that of, say, the Spanish Civil War. In NI, nationalists and republicans are assumed to be (broadly) on the same side. In Spain, they were mortal enemies. This is due in part to the malleable nature of republicanism as a concept — republican movements have often encompassed wide variations in political opinion — but is also telling of how the central political conflict in Northern Ireland has appropriated political concepts to fit the purposes of its protagonists.
Classical republicanism is an enlightenment ideology concerned with essential liberty and the fight against tyranny. The central concept is that of the social contract, where all citizens regardless of creed, class or any other distinction, consent to be bound by the rules of society in order to obtain the mutual benefits of security and prosperity. These universalist ideals were hard fought for, but are uncontroversial in 21st century Europe — it could be argued that under this definition even the constitutional monarchies are “republican”, although (unlike Rousseau) modern republicans would certainly balk at any suggestion of inherited power.
The corollary of the social contract, the right of the people to revolt against a regime that violates the contract, is more problematic. This concept is the claimed root of modern Irish Republicanism, but the identification of injustice is by itself insufficient — one also needs someone to revolt on behalf of. Does every individual have the right to rebel against unjust authority, or only if he can gather enough friends? Who constitute a “people” for the purposes of revolt – a nation, a region, a social class? In the Spanish Civil War, it was largely a social class who revolted against the aristocratic Nationalists. In Northern Ireland by contrast, the oppressed people were defined by nationalism.
While Irish Republicanism has consistently claimed to be struggling on behalf of all the people of Ireland, whether Catholic, Protestant or Dissenter, it has long been de facto an Irish nationalist movement. This is an important distinction: while there have been many prominent Protestants in the Republican movement, they have all self-identified as Irish. Those people who do not self-identify as part of the Irish nation have played a vanishing role. As anyone familiar with the Balkans can attest, religion plays a large part in national identity, and the nationalist movement of the late 19th century left most Protestants, particularly those in Ulster, cold. As Protestants drifted away from an increasingly Catholic, Gaelic nationalism, the Republican movement that relied on nationalism for its legitimacy lost its claim to universality — and republicanism without universality is a contradiction in terms.
Unionism never pretended to be a universalist doctrine, but it too has drifted away from its roots. The Irish Unionism of the 19th century emerged from the Whig aristocracy, while its sister Ulster Unionist movement was (and still is) based in the industrial heartland. What unified them was a shared concern for the economy of an Ireland cut off from its trading partners by new tariffs, but they differed in important ways — Ulster Unionists, particularly Presbyterians, were more exercised by the fear of a Catholic-majority state than the Dublin-based (and predominantly Anglican) Irish Unionists. After the establishment of the Free State, Irish Unionists saw their economic interests as best defended by Cumann na nGaedheal and Dublin-based unionism faded away.
In Northern Ireland, the traditional unionist concern for the economy is consistently raised, whereas fear of domination by the Catholic Church, still explicit on the fringes, has evolved into a counter-nationalism — while a hundred years ago northern Protestants called themselves Irish, soon they began to self-identify as Ulster-British. The Irish Unionist concern for the well-being of the island economy was replaced by relief, even schadenfreude, at the economic disparities between North and South. Cut off politically from its erstwhile allies in Dublin, Ulster Unionism became increasingly parochial. Partition, accepted with reluctance by Carson, became a shibboleth. Home Rule from Dublin was anathema, but once transplanted to Belfast it was quickly embraced. Modern Unionism, in its popular form at least, is for most practical purposes merely an Ulster-British nationalism.
There are exceptions, of course. There is a notable integrationist streak in unionism, although this is much less vocal now that all the major parties have signed up to the Agreements and devolution for NI is no longer a special case. There is also a prominent “Liberal Unionist” presence amongst the cognoscenti, which has recognised the nationalist element in unionism as a destructive influence and seeks to reclaim the intellectual high ground. Yet neither of these movements is truly universalist — they are still primarily a rearguard action against further erosion of that which exists today. Even the liberal unionists are hostages to Caledonian fortune — a sovereign Scotland would in many ways be a more comfortable bedfellow for Northern Ireland than a rump Englandandwales, but that discussion remains taboo.
So can unionism and republicanism be reconciled? It is clear that as currently formulated they cannot. This is not due to the inherent principles of unionism or republicanism, but rather to the ethno-nationalist conflict that they have been grafted onto. There are only two ways that a internecine conflict can be resolved: either one nationalism defeats and subdues the other, or both can submit to the creation of a new, shared identity. In Northern Ireland the former has been tried with disastrous results, while the latter shows no sign of progress. Nationalism, whether Irish or Ulster-British, is the irreconcilable baggage that must be discarded in the search for a political synthesis.
If republicanism in NI wishes to reclaim universality, then republicanism and Irish nationalism must be divorced. Those who would prioritise Irish unity over reconciliation should properly be called nationalists, while true (classical) republicans are those who would seek a renewed social contract within whatever borders are realistically available. This is almost exactly the converse of the positions of the so-called “republican” and “nationalist” parties, but more consistent with the use of terminology outside Ireland.
Unionism must also ditch its nationalist past, but it must also free itself from sentimental attachment to one particular form of union. A universalist unionism would embrace political co-operation with anyone willing to engage on reasonable terms, whether inside the UK or beyond. The EU is a union of a different character, but the basic principle of diverse polities uniting to mutual benefit is the exact same one that unionism holds dear. A multiplicity of relationships is a strength, not a weakness.
We can thus regard unionism and republicanism as complementary — republicanism stresses the common bond between individuals within a society, and unionism expounds the bonds between societies. One concerns itself with equality within, and the other equality without. While nationalism sets neighbour against neighbour, unionism and republicanism share a common interest in building bridges. What both lack is the confidence to step back from the entrenched conflict of nationalisms and engage on matters of universal principle rather than parochial dogma.