After his passport was returned to him, Chinese contemporary artist Ai Weiwei was able to leave his Beijing studio for Berlin. (Zachary Bako/For The Washington Post)

— Ai Weiwei is now free to travel, but he is hardly free.

Last week, Chinese officials returned his passport, ending a four-year travel ban. On Thursday, the art-world darling and Chinese-government critic boarded a flight to Germany to visit his 6-year-old son.

But even as Ai set off, he remained, in many ways, stuck in place, locked in the same, strange purgatory he has inhabited since his 81-day detention in 2011. His is a world where surveillance is constant and certainty is scarce.

He does not know why, for instance, after 600 days of protest, authorities restored his right to move around or why the British government denied his request for a six-month visa on the grounds that he failed to disclose a “criminal conviction,” when, under Chinese law, he has none.

Nor does he understand why Chinese authorities chose to loosen his leash while they are locking up other critics — lawyers, activists and artists — by the dozen. “We used to think that everything has a reason, or some history to it, but that’s not China,” he said in an interview at his Beijing studio Tuesday.

“Freedom is a struggle, it’s continuous, and it’s a result we may never really get,” he said.

China’s most famous artist has spent much of his life testing the limits of free expression in the country, and musing, very publicly, about the results.

Ai, the son of a renowned Chinese poet who was exiled in the Cultural Revolution, is a longtime critic of the ruling Communist Party. In the run-up to the 2008 Summer Olympics in Beijing, he consulted on the design of the “Bird’s Nest” stadium, but he later denounced the Games as a “fake smile,” drawing ire from authorities.

He launched a “citizen investigation” into the deaths of thousands of schoolchildren in the 2008 Sichuan earthquake, gathering their names against the government’s wishes and turning tiny backpacks into installation art displayed around the world.

Ai was attending the trial of a fellow earthquake activist in 2009 when he was beaten by police officers until his brain bled. He posted a picture of himself with a tube in his head and a bag of blood in his hand.

Not two years later, amid a crackdown on dissent spurred by the Arab Spring, he was hooded, thrown into the back of a van and held for more than two months.

Then came an interminable period of “probation,” in which, he told The Washington Post last year, he was sometimes forced to “check in” with officials “20 or 30 times a day.”

Police promised to return his passport “too many times,” Ai said Tuesday. While he waited, he created major exhibitions, including his recent show at the infamous Alcatraz prison, remotely.

He also turned his confinement into a sort of high-stakes art project, a living comment on what it means to be watched, to wiggle, sometimes gleefully, under the government’s thumb.

Ai has been under incredible surveillance, so much so that he calls the security officials assigned to monitor him “colleagues.” They watch him sleep, he said, sift through his correspondence and listen to his conversations. “Nobody else cared about me that much,” he joked.

To counter that invasion, Ai broadcast his life on his own terms. He is a prodigious poster of selfies and a lively presence on social media. When “Gangnam Style” went viral, Ai starred in a raucous parody video called “Grass Mud Horse Style,” a reference to a crass pun that’s also an anti-censorship meme.

In the international news media, Ai is often called “fearless” — and in many ways he seems it.

But he is also a protective father of a 6-year-old son. He posts pictures of their video chats on Instagram and talks, warmly, of the boy’s imaginings. He is “my weakness,” Ai said.

When the passport news broke, one journalist wondered out loud whether the government was offering an “invitation to exile” and whether Ai would take it. Artnet News went so far as to ask: “Is Ai Weiwei moving to Berlin?

Two days before he set off for Germany, Ai was vague about his plans. Perhaps that’s because, as he put it, he likes to be surprised. Or maybe the outspoken artist has learned, at last, to keep some things to himself.

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