For Joe Biden, the four-day visit to Ireland that started last Wednesday offered an opportunity to celebrate his roots and bask in the reflected glory of a landmark peace agreement that a former US president and an ex-senator, both members of his Democratic Party, played key roles in getting over the line. But as citizens north and south of the Irish border mark the 25th anniversary of the Good Friday Agreement, history also owes a nod to the Republican éminence grise of US foreign policy: Henry Kissinger.

The 99-year-old Kissinger played no active part in the Irish peace process, but a negotiating tactic that is generally credited to the former secretary of state was a crucial element in bridging the gap between the two sides: constructive ambiguity. Wording the agreement in such a way that both parties were able to project the meaning they wanted on to it enabled decades of sectarian violence that had claimed more than 3,500 lives to finally end. While Kissinger is a controversial figure, the success of that approach stands as a rare beacon of diplomatic finesse in an era of increasingly intractable conflicts and heightening tensions — from Ukraine to the South China Sea.

Constructive ambiguity is the essence of pragmatic flexibility. The deliberate use of imprecise language aims to sidestep sensitive topics in the hope that once an agreement has been reached, further progress will follow. It enables the process to move forward without getting hung up on points of irreconcilable difference. In that sense, it is an act of faith in the capability of willing participants to find a way forward. Retaining flexibility of interpretation also gives political cover to the negotiating parties who will have to sell concessions to hardliners.

One of the best-known examples dates from the Six-Day Arab-Israeli War of 1967. United Nations Resolution 242 of November that year required the withdrawal of Israeli armed forces “from territories occupied in the recent conflict”. Omitting “the” before territories left it unclear whether Israel was obliged to withdraw completely or only partially, political scientists Geoff Berridge and Alan James write in A Dictionary of Diplomacy. Kissinger employed the tool on numerous occasions, including in the 1972 Shanghai communique, which contained an ambiguity on the US’s position on “one China”, and in the Paris Peace Accords that aimed to bring the Vietnam War to an end the next year.

Constructive ambiguity has its detractors. A less complimentary term might be “fudge” and, in fairness, the tactic has a patchy record of achievement. The Paris accords did not keep the peace in Vietnam, and perceptions that Washington is shifting its position on the one-China policy have become a flashpoint in deteriorating relations with Beijing. The most potent argument against the approach is that it is inherently deceptive. Advocates of precision in language may reasonably ask whether an agreement can be said to exist at all if the participants are unclear about what exactly they are agreeing to. For those focused on practical results, though, this misses the point.

“Amateur analysts often invoke the ambiguity of such agreements as a demonstration of the confusion or the duplicity of the negotiators — a charge later levelled against the 1973 Paris Peace Accords,” as Kissinger wrote in his 1994 book, Diplomacy.

“Yet, most of the time, ambiguous documents such as the Geneva Accords reflect reality; they settle what it is possible to settle, in the full knowledge that further refinement must await new developments. Sometimes the interlude permits a new political constellation to emerge without conflict; sometimes the conflict breaks out again, forcing each party to review its bidding.”

By this measure, the Good Friday Agreement must be counted a triumph. The document’s sleight of hand on issues such as the decommissioning of weapons by paramilitary groups was unambiguously vindicated by the decline in violence that followed in the years after its signing. Northern Ireland today is a province transformed: army checkpoints have gone, investment has risen and the economy has revived — leaving aside Covid effects. A return to the 30 years of the Troubles, as they are known, is by common assent unimaginable.

Constructive ambiguity “carved out the time and space necessary for both sides of the conflict to come to believe, credibly, that they could fulfil their political agendas without recourse to violence,” said Noel Anderson, an assistant professor at the University of Toronto and author of the paper, The Art of the Fudge: Merits of Constructive Ambiguity in the Good Friday Agreement.

“Over time, new norms of nonviolence became entrenched, intercommunal relations were strengthened, and the overall security situation dramatically improved.”

This is not to suggest that constructive ambiguity was entirely responsible. Both the province’s republicans, who seek a united Ireland, and the unionists, who want Northern Ireland to remain a part of the United Kingdom, made major concessions. Ireland rewrote its constitution to remove its territorial claim to Northern Ireland, while the UK agreed to hold a referendum in the province if it ever appears that a majority favour reunification.

Without recourse to creative wording, though, final agreement might never have been reached. One of the biggest areas of ambiguity was disarmament. The agreement appeared to imply that decommissioning was an essential part, but did not actually say that, merely noting that all participants confirmed their intention to “use any influence they may have” to achieve this. The parties could have stayed in Belfast’s Castle Buildings where the talks were held “for three years rather than three days and nights” without bridging the gap, Jonathan Powell, then the UK’s chief government negotiator, wrote in 2017.

The course of post-Good Friday events suggests there can be an inestimable value in reaching an agreement on something — anything — while glossing over stumbling blocks. The act of coming to a deal changes the energy in a relationship. Decades of enmity can melt away. Democratic Unionist Party leader Ian Paisley and former Irish Republican Army commander Martin McGuinness worked together so amiably as first minister and deputy in the power-sharing Northern Ireland Assembly that they were nicknamed the “Chuckle Brothers”. The images of the late pair laughing together would once have been inconceivable.

In the run-up to the 25th anniversary and Biden’s visit, British media have struck a sometimes gloomy note, observing the legacy of political dysfunction, the destabilising impact of the Brexit vote and the related threat of a resurgence in violence. This, though, does not invalidate the historic achievement of the Good Friday Agreement. As George Mitchell, the US senator who was one of the primary architects of the deal, said: “It is important to recognise that the agreement does not, by itself, provide or guarantee a durable peace, political stability or reconciliation. It makes them possible.”

• Matthew Brooker is a Bloomberg Opinion columnist covering business and infrastructure out of London. A former editor and bureau chief for Bloomberg News and deputy business editor for the South China Morning Post, he is a CFA charterholder