In the six months since she came to office charged with carrying out the mandate of the British referendum to quit the European Union, Prime Minister Theresa May has seemed indecisive and ambiguous about how this might be achieved. That ended Tuesday, when she made clear that Britain intends to leave the single market, the central feature of the historic effort to eliminate all barriers to trade across the union and to uphold the free movement of goods, services, capital and — the one Britain could not swallow — people.

Whatever one makes of Brexit, it is critical to ensure that this extraordinarily complex divorce does as little damage as possible to long-term economic and political relations between Britain and the Continent. So May’s speech is to be welcomed for spelling out her government’s intentions on the core issue before it formally triggers the two-year exit process, which the prime minister has said she will do by the end of March.

In effect, May confirmed what had become increasingly clear: that the core demands of the Brexiteers — an end to the free movement of the bloc’s citizens and to the jurisdiction of the European Court of Justice over British law — are incompatible with core tenets of the European Union.

Ending uncertainty at least on that score sent the pound surging. May also sought to diffuse a smoldering constitutional clash by pledging to give both houses of Parliament a vote on the final deal. She made no reference, however, to a pending ruling by the supreme court on whether Parliament must vote on the formal notification to the union, and there is no certainty that legislators would support her on either vote.

On the EU side, Donald Tusk, the president of the European Council, seemed to sum up the predominant reaction in this tweet: “Sad process, surrealistic times but at least more realistic announcement on #Brexit. EU27 united and ready to negotiate after Art. 50.”

That may indeed be a measure of our times, that a dollop of realism becomes welcome news. But while May took the single market off the table and insisted that Britain would cut its own deals outside the bloc, she said she would still seek to maintain some tariff-free access to European markets. She also said she would seek transitional arrangements for financial services and businesses past the two-year deadline for completing exit talks.

All that may be hard for the union to accept.