Alliance deputy leader Stephen Farry has said that many members of the party are "open to persuasion" on Northern Ireland's constitutional future.
He told the party's annual conference in Belfast that while there currently was not a case for a border poll, it was "a very fluid situation and multiple active debates are under way".
Mr Farry delivered the keynote speech at the event after party leader Naomi Long was diagnosed with a severe lung infection and could not attend.
Addressing around 300 delegates, he said his party was "conscious of calls for wider change across these islands" and that Brexit had "energised the debate around the constitutional question".
Alliance would "engage with confidence" in "civilised, rational and evidence-based discussions", he said.
It was a genuinely cross-community party, proud and self-confident of its identity as opposed to one where unionists and nationalists co-existed uneasily, Mr Farry said.
"While there may be some members who prefer the Union, and some who prefer a united Ireland, and indeed many who are open to persuasion, we are not only united, but defined, by our shared commitment to make this society work, to overcome division and to build a better future," he said.
"We don't believe there is currently the case for a border poll, and nor are we pursuing one, but we do recognise that there is a very fluid situation and multiple active debates are under way."
Mr Farry told the conference, which marked the party's 50th anniversary, that people in Northern Ireland were moving away from traditional labels.
He attributed his party's success in last year's council, EU and Westminster elections to more people expressing open, mixed and multiple identities.
He said Northern Ireland was "a changing society, and changing more quickly than many appreciate".
Alliance was helped by having "called Brexit correctly, right from the start, being consistent throughout". The "old canard" of a vote for Alliance being a wasted one had been shattered, Mr Farry said.
"We have proven that we can win anywhere in Northern Ireland. And we have drawn votes from right across the community," he added.
"We have proven that in a political context usually framed around the constitutional question and a clash of identities that a liberal and cross-community party can not only survive but flourish. But while we have broken the glass ceiling, there can be no room for complacency or sitting back on our laurels," he said.
"Brexit is set to dominate the political, economic and security context for at least the next decade. We were proud Remainers and we remain passionate Europeans today and into the future.
"We should look forward and aspire to Northern Ireland rejoining the EU sooner rather later."
Mr Farry said that Prime Minister Boris Johnson was set to "pursue a reckless hard Brexit".
"The Brexit extremists exhibit the characteristics of revolutionaries, in this case fuelled by a libertarian ideology and wishful, delusional thinking," he said.
"Like most revolutions, it will at some point run out of steam or destroy itself, but for now a collision course has been set with the EU with an irresponsible and workable prospectus for a future relationship."
Mr Farry described the protocol as "a front stop". He added: "The protocol is part of the Withdrawal Agreement, and failure to implement it not only undermines the UK's ability to negotiate free trade agreements but also risks leaving Northern Ireland as a 'no man's land', with the Good Friday Agreement undermined and a renewed risk of the return of a hard border on this island."
He said that the New Decade, New Approach deal, which saw the return of devolution, was far from perfect but it was a starting point.
He said Stormont must press the Government for more funds for Northern Ireland "based on our legacy of division and violence, and the legacy pressures that flow from that".
But the Executive "shouldn't be afraid of our feet being held to the fire on reform".
He said the Bengoa proposals for the health service had to be delivered and that education also needed "Bengoa-style reforms".