“I only speak two languages — English and bad English,” says Bruce Willis as the cab-driving cosmic hero of the sci-fi action film “The Fifth Element.” Now, it seems, Willis can no longer speak even that much.

On Wednesday, an Instagram message posted by his family announced that Willis has retired from acting because he is losing his ability to use speech. “Our beloved Bruce has … been diagnosed with aphasia, which is impacting his cognitive abilities,” the message reads. “As a result of this and with much consideration Bruce is stepping away from the career that has meant so much to him.” Willis’s ability to memorize scripts and maintain focus had declined alarmingly in recent years. On movie sets, his lines had to be fed to him through an earpiece. “He just looked so lost,” one studio supervisor told the Los Angeles Times.

Aphasia is a disorder that robs people of their basic communication skills. It affects the area of the brain that controls language and the ability to speak, write, or understand words. Aphasia can make it impossible to remember the names of common objects or to verbalize even simple sentences. People with aphasia may know exactly what they want to express, yet be unable to articulate the words they need. They may find themselves at a loss to make sense of even the simplest written words. For anyone inflicted with aphasia, the experience can be distressing, excruciating, disorienting, or frightening. But for someone whose livelihood and persona are based on words — like an actor, a broadcaster, or a writer — aphasia is uniquely nightmarish.

When the novelist, poet, and essayist Paul West had a stroke in 2003, the resulting aphasia toppled him, as his wife Diane Ackerman put it, into a “private hell” diabolically tailored to destroy his greatest talents.

“The author of more than 50 stylishly written books, a master of English prose with the largest working vocabulary I’d ever encountered, a man whose life revolved around words, he had suffered brain damage to the key language areas of his brain and could no longer process language in any form,” Ackerman wrote in The American Scholar. It afflicted him with “the curse of a perpetual tip-of-the-tongue memory hunt” and for a time “all he could utter was the syllable ‘mem.’ Nothing more.”

When H.L. Mencken was stricken with aphasia in 1948, his friends and loved ones “were stunned by the grotesque irony of it,” wrote Terry Teachout in his biography of the towering and journalist. “All he could do now was sign his name, scrawl an occasional one-sentence note full of misspelled words, and recognize the names of people he knew when he saw them in the paper.” Only with difficulty could Mencken still make himself understood. He was devastated by the realization that his career was over. Above all he was shattered by the fact that he could no longer read, and began referring to himself in the past tense, as if he were already dead.

It isn’t only strokes that can cause aphasia. The disorder can come on gradually because of a brain tumor or a degenerative condition. It can also occur in temporary episodes, brought on by seizures or, as I have reason to know, by severe migraine headaches.

I have been getting migraine attacks since I was 8 or 9 years old, and am only too familiar with the pain, nausea, and partial blindness that accompany them. The very worst attacks, the ones I have always found especially alarming, also cause transient aphasia. I suddenly find that I cannot summon basic words. I am unable to understand the meaning of anything I try to read, and struggle to string together even the simplest sentences. Fortunately, these episodes of aphasia usually retreat within two or three hours, but they are intensely disquieting while they last. In the back of my mind there is always the slightly panicky thought: What if this time the symptoms don’t subside?

Once I was in the middle of a live TV interview when a migraine attack began and my words started to slip away from me. I recall trying to say something about “journalists,” but it kept coming out as “nerjalists.” On another occasion, the aphasia struck as I was taking questions from an audience after a speech. I had no trouble understanding the questions, but when I tried to formulate answers, the words kept slipping out of my grasp. The next day, I called the organizer of the event to apologize and she rebuked me for not telling the audience what was happening at the time. “They would all have understood,” she said. (She was right: I had been speaking to a doctors’ group.)

Disturbing as such experiences can be, they are nothing next to the ordeal of someone like Willis, who is undergoing the gradual disappearance of the language and speech gifts that have been at the center of his public life and knows they won’t be coming back. Willis leaped to fame in the 1980s, when he co-starred in the ABC comedy-drama “Moonlighting.” He portrayed the wisecracking private detective David Addison alongside Cybill Shepherd, who played his beautiful partner, Maddie Hayes. The plotlines were fine, but what made the show such a hit was the dialogue — playful, sparking, witty, arch, with lines that overlapped and threw off an endless shower of will-they-won’t-they double entendres.

“You took the words right out of my mouth,” says David in one episode.

“Open up,” replies Maddie. “I’ll put ‘em back.”

Tragically, there is no one now who can put back the words that Willis is losing. Aphasia is cruel to all of its victims, but I can’t help thinking that the torture is worst for those who spent a lifetime making their name with words. My heart goes out to Willis and to all who find themselves deprived of the language they always took for granted. May they be compensated for their awful loss with the love and support of all who care for them.

(Jeff Jacoby is a columnist for The Boston Globe).