A CHINESE GOVERNMENT spokesman expressed shock at comments Japanese Prime Minister Shinzo Abe made during a recent interview with The Washington Post regarding China’s motivations. A reading of Mr. Abe’s full remarks (available on our Web site) would show that shock is not called for. Mr. Abe, on the eve of his Friday visit with President Obama, delivered a cogent explanation of China’s growing assertiveness — and also of why he believes there is reason to hope for Chinese restraint.

Mr. Abe noted that Communist Party rule ordinarily would base its legitimacy on a promise of equality. Having embraced the free-market economy, the party can no longer make such a promise, so it bases its legitimacy on two other pillars: economic growth and patriotism, the latter unfortunately fueled by a fair dollop of anti-Japanese sentiment. With the education system teaching that sort of patriotism, he said, the government can gain popularity with actions such as its provocative challenges of Japanese control of disputed islands in the East China Sea.

What then are the grounds for hope? Mr. Abe noted that provocative behavior at sea threatens the trust of China’s trading and investing partners, which in turn could endanger its first pillar, economic growth. He said Chinese leaders may come to understand that. In the meantime, he said, it is important to maintain the strength of the U.S.-Japan alliance, which Mr. Obama and Mr. Abe indeed reaffirmed during their Friday meeting.

A key way to strengthen the bilateral relationship, and to show that it is not just a military alliance, would be for Japan to join talks on an incipient Pacific trade agreement — and that prospect also received a boost in the Friday summit. The Trans-Pacific Partnership (TPP), led by the United States, includes nations from Canada to Brunei but not, so far, Japan, the world’s third-largest economy (after American and China). Joining the TPP would boost not only the alliance but also Mr. Abe’s hopes of modernizing and opening Japan’s economy. But as in all countries, special interests that might be harmed by free trade are more focused in opposition than the broader populace, which would receive a larger but more diffuse benefit, is in support.

As a result, it was valuable that Mr. Obama made clear that, while the TPP countries will make no exceptions to entice Japan into the talks, they also will set no disqualifying preconditions, and Japan will be free to negotiate vigorously in its own interest. With a crucial July election looming, Mr. Abe still faces a difficult political choice. But if he wants to join — and he told The Post that “a free trading environment would be in the national interest of Japan” — he comes home with a strengthened case to make.