The smell was strange. Sharp. Chemical. Wrong. The concrete wall was too close. My glasses were gone. One of my kids was standing on the sidewalk next to our car—not crying, just confused.

The seat belt had held. The crumple zone had crumpled. The airbag had fired. Everything designed to protect bodies had done its job. But the car, a Tesla Model X, was totaled.

One Sunday last fall, my kids and I were on a drive we’d done hundreds of times, winding through the residential streets of the Bay Area to drop my son off at his Boy Scouts meeting. The Tesla was in Full Self-Driving mode, driving perfectly—until it wasn’t.

What happened next, I’ve had to piece together. My memory is hazy, and some of it comes from one of my sons, who watched the whole thing unfold from the back seat. The car was making a turn. Something felt off—the steering wheel jerked one way, then the other, and the car decelerated in a way I didn’t expect. I turned the wheel to take over. I don’t know exactly what the system was doing, or why. I only know that somewhere in those seconds, we ended up colliding with a wall.

You might think I’d have known what to do in this situation. I used to run the self-driving-car division at Uber, trying to build a future in which technology protects us from accidents. I had thought about edge cases, failure modes, the brittleness hiding behind smooth performance. My team trained human drivers on when and how to intervene if a self-driving car made a mistake. In the two years I ran the division, we had no injuries in our early pilot programs.

With my own Tesla, I started out using Full Self-Driving as the default setting only on highways. That’s where it makes sense: You have clear lane markers and predictable traffic patterns. Then, one day, I tried it on a local road, and it worked well enough to become a habit.

Despite the accident, we were lucky. I walked away with a stiff neck, a concussion, a few days of headaches, and some memories I can’t shake. The kids climbed out unharmed. Still, you could say I was crushed in what the researcher Madeleine Clare Elish calls the moral crumple zone. Some parts of a car are specifically designed to absorb damage in a crash, to protect the people inside. But when complex automated systems fail, Elish argues, it’s the human users who take the blame. My car’s Full Self-Driving mode logged flawless miles for three years, but when the accident happened, it was my name on the insurance report.

And the car has evidence. While you’re at the wheel, it logs your hand position, your reaction time, whether you’re keeping your eyes on the road—thousands of data points, processed by the vehicle. After crashes, Tesla has used these data to shift blame onto drivers. Following a fatal collision in Mountain View, California, in 2018, the company released a statement in which it noted that “the vehicle logs show that no action was taken.” (Tesla did not respond to a request for comment.)

While Tesla can access these records, it’s not so easy for drivers. They can request their data, but some say they’ve received only fragments—and have had to go to court to get more. When plaintiffs in a Florida wrongful-death case sought key evidence of how one of Tesla’s driver-assistance systems had failed, the company said it didn’t have the data. The plaintiffs had to hire a hacker, who recovered them from a computer chip in the crashed vehicle. Later, Tesla stated that the data had been sitting on its own servers for years, and that the company failed to locate them by mistake. (A judge did not find “sufficient evidence” to conclude that Tesla had sought to hide the data.)

For now, the legal principle is simple: You’re responsible. Though Tesla originally called its technology “Full Self-Driving Capability,” the system is officially classified as “Level 2” partial driver automation, which means the human must remain in control at all times. Last year, a judge in California found Tesla’s original name “unambiguously false” and misleading to consumers; Tesla now uses “Full Self-Driving (Supervised).” When a Tesla using a version of the technology killed two people in California in 2019, the car’s own logs were used to prosecute the driver for failing to prevent the crash—not the company that designed the system. The company was held accountable in a major verdict for the first time only last year, when a jury found Tesla partly liable in the Florida wrongful-death case and awarded $243 million to the plaintiffs.

A similar pattern is emerging everywhere algorithms are asked to work alongside humans: in our inboxes, our search results, our medical charts. These systems are building toward full automation, but they’re not there yet. Computers still regularly make mistakes that require human oversight to avoid or fix.

Full Self-Driving works almost all of the time—Tesla’s fleet of cars with the technology logs millions of miles between serious incidents, by the company’s count. And that’s the problem: We are asking humans to supervise systems designed to make supervision feel pointless. A machine that constantly fails keeps you sharp. A machine that works perfectly needs no oversight. But a machine that works almost perfectly? That’s where the danger lies. After a few hours of flawless performance, research shows, drivers are prone to start overtrusting self-driving systems. After a month of using adaptive cruise control, drivers were more than six times as likely to look at their phone, according to one study from the Insurance Institute for Highway Safety.

Tesla’s description of Full Self-Driving on its website warns, “Do not become complacent,” and I didn’t think I was. Before my accident, I had my hands on the wheel. But I was driving the way the system had conditioned me to: monitoring instead of steering, trusting the software to make the right call. The familiarity curve bends toward complacency, and the companies building these systems seem to know it. I certainly did. I got lulled anyway.

Psychologists call this the vigilance decrement. Monitoring a nearly perfect system is boring. Boredom leads to mind-wandering. The research is unforgiving: Drivers need five to eight seconds to mentally reengage after an automated driving system gives control back. But emergencies can unfold much faster than that. The driver’s physical reaction might be instantaneous—grabbing the wheel, hitting the brake. But the mental part? Rebuilding context, recognizing what’s wrong, deciding what to do? That takes time your brain doesn’t have.

The driver in the 2018 Mountain View accident had six seconds before his car steered itself into a concrete median. He never touched the wheel. That same year in Tempe, Arizona, sensors in an Uber test vehicle detected a pedestrian nearby with 5.6 seconds of warning. The safety driver looked up and took the wheel with less than a second left. By then, it was just physics.

In my case, I did take action before my accident. But I was asked to snap from passenger back to pilot in a fraction of a second—to override months of conditioning in the time it takes to blink. The logs would show that I turned the wheel. They wouldn’t show the impossible math.

I don’t know enough about what actually happened during my accident to say that Tesla’s technology crashed the car. But the problem is bigger than one company’s self-driving system. It’s about how we’re building every AI system, every algorithm, every tool that asks for our trust and trains us to give it. The pattern is everywhere: Condition people to rely on the system. Erode their vigilance. Then, when something breaks, point to the terms of service and blame them for not paying attention.

My car didn’t warn me when it was confused. Chatbots don’t, either; they deliver their results in the same confident voice, whether they’re right or hallucinating. They perform expertise, even when the sources they cite are dubious or fabricated. They use technical language in an authoritative tone. And we believe them, because why wouldn’t we? They’ve been right so many times before.

Cars train us mile by mile; AI trains us week by week. In week one, you read a chatbot’s output carefully. By week three, you’re copying and pasting without reading. The errors don’t disappear, but your vigilance does. So does your judgment, until one day you realize that you can’t remember which ideas in a memo were yours and which were generated by AI. What does it say about us that we’ve handed over our thinking so willingly?

[Read: The people outsourcing their thinking to AI]

When my car failed, it was immediate and palpable. With chatbots, the failure is silent and invisible. You find out about it later, if at all—after the email is sent, the decision made, the code shipped. By the time you catch the mistake, it’s already out there with your name on it. When the system works, you look efficient. When it fails, your judgment is questioned, sometimes with catastrophic consequences. In 2023, a New York lawyer was sanctioned for citing six cases that didn’t exist. ChatGPT had invented them, but he’d trusted it, and the court blamed him, not the tool. Because a chatbot never gets fired.

We’re experiencing an uncanny valley of autonomy. Computer systems aren’t just almost human; they are almost capable of working on their own. When they fail, someone has to absorb the cost. Right now, that someone is us. But when we pay for a self-driving car or an AI tool, we think we’re buying a finished product, not signing up to test a work in progress.

This “almost” phase isn’t a brief transition. It’s the product—one that will be with us for years, maybe decades. So it’s important to notice the patterns. When an AI system never admits uncertainty, or when a car’s marketing says “self-driving” but the fine print says “driver responsible,” that’s a warning sign. When you realize that you haven’t really been paying attention for the past 10 miles, or the past 10 auto-composed emails, that’s the trap.

Things don’t have to be this way, but they won’t change unless consumers see the situation clearly and refuse to accept it. We should reject the deal we’ve been handed—the one where the terms of service become a shield for companies and a sword against users. We should demand that companies share the risk they’re enticing us into taking. If they design for complacency, they should get some of the blame when their product fails.

This isn’t a utopian goal. In July 2025, the Chinese carmaker BYD announced that it would pay for the damage caused by crashes involving its self-parking feature, sparing the driver’s insurance and record. It’s only one company, and only one feature, but it proves that accountability is a choice. Other businesses can be persuaded to opt in, too.

My kids were in the back seat when I had my car accident. One day, they’ll have their own cars and use AI in ways that I can’t even imagine yet. The systems they inherit will be built either to elevate them or to lull them and blame them when things go wrong. I want them to notice when they’re being trained. I want them to ask who absorbs the cost, and the damage.

This article appears in the April 2026 print edition with the headline “My Self-Driving Car Crash.”

On the third day of the war in Iran, Defense Secretary Pete Hegseth called Operation Epic Fury the “most-precise aerial operation in history.” A difficult claim to fact-check. More difficult still has been parsing statements from the White House and the Pentagon to figure out, with any exactitude, why we are at war in the first place. So far, the Trump administration has offered at least 10 separate rationales in just six days.

Let’s start shortly after the first missiles launched early Saturday morning. In an eight-minute address posted soon after to his social-media platform, President Trump outlined a few explanations.

The reason for war, he said, is to eliminate “imminent threats” from the Iranian regime—threats that “directly endanger the United States, our troops, our bases overseas, and our allies throughout the world.” (Let’s call this Rationale No. 1: the imminent threat.) Also, he said, the objective is to ensure that the regime “can never have a nuclear weapon.” (Rationale No. 2: no nukes.) Also, he added, the objective is to “ensure that the region’s terrorist proxies can no longer destabilize the region or the world.” (Rationale No. 3: halt the militias.) These goals are not incompatible, of course, and all involve degrading Iran’s ability to project force beyond its borders.

But just as he appeared to be wrapping up, Trump floated a major new reason: laying the groundwork for the Iranian people to “seize control of your destiny, and to unleash the prosperous and glorious future that is close within your reach.” In other words, “Take over your government.” (Rationale No. 4: regime change.) A couple of hours later, Trump said his attention was steadfastly on this last explanation—securing the liberty of the Iranian people from the country’s 47-year theocratic regime. “All I want is freedom for the people,” he told The Washington Post just after 4 a.m.

About half an hour later, another justification was evidently on the commander in chief’s mind: “Iran tried to interfere in 2020, 2024 elections to stop Trump, and now faces renewed war with United States,” he wrote on Truth Social. The post included a link to a story in a right-wing media outlet purporting to show Iranian election interference. (That seemed enough to constitute Rationale No. 5: election interference, before the sun had even risen over Mar-a-Lago.)

Later on Saturday, Trump revisited his second and third rationales for the strikes in an interview with Axios. He cited the failure of negotiations (led by his son-in-law Jared Kushner and the real-estate developer turned Middle East envoy Steve Witkoff) to reach a deal to end Iran’s nuclear ambitions. And he also spoke about his realization, while writing his speech the day before the bombing started, that Iran had a history of violence in the region: “I saw that every month they did something bad, blew something up or killed someone.”

By Saturday afternoon, though, the president was ready to unveil his most ambitious rationale yet. As reports filtered in about the assassination of Supreme Leader Ali Khamenei, Trump took to social media again to declare that the operation would continue “as long as necessary to achieve our objective of PEACE THROUGHOUT THE MIDDLE EAST AND, INDEED, THE WORLD!” (Rationale No. 6: world peace, an appropriately grand finale for launch day.)

On Sunday morning, Trump was back to Rationale No. 2, preventing Iran from developing nuclear weapons—with little time to spare, apparently. “If we didn’t do that, they would have had a nuclear weapon within two weeks,” the president told Fox News, citing a time frame he had not included in his initial remarks. The same morning, the president told NBC News that the reason for the launch was simple: “They weren’t willing to say they will not have a nuclear weapon.”

(For context: The White House had announced last June that Iranian nuclear facilities had been obliterated and “suggestions otherwise are fake news.” An analysis of satellite images by The New York Times last month showed repairs at key missile sites began shortly after those attacks last summer, but that work at nuclear facilities had been slower and more limited. And the head of the International Atomic Energy Agency said Monday that, although Iran has the ambition to possess nuclear weapons, it does not have a “structured program” to build them.)

As for supporting the Iranian people’s freedom and pushing for regime change (Rationale No. 4), Trump on Sunday seemed to rhetorically retreat. “What we did in Venezuela, I think, is the perfect, the perfect scenario,” he told The New York Times, referencing the middle-of-the-night capture of Venezuelan President Nicolás Maduro in January and the administration’s willingness since then to work with Maduro’s second-in-command, Delcy Rodríguez. Asked whether the U.S. would defend Iranians if they sought to overthrow the current regime (as Trump had encouraged them to do the day before), he said, “I don’t make a commitment one way or the other.” And the same morning, he told our colleague Michael Scherer that he had agreed to talk to Iranian leaders after they failed to agree to a deal. “They should’ve done it sooner,” Trump said. “They played too cute.”

Shortly after, a prerecorded announcement appeared on Truth Social in which the president emphasized that “combat operations” will be ongoing “until all of our objectives are achieved.” The explanation built on the global-peace idea of Rationale 6 with a look to the future: “We’re undertaking this massive operation not merely to ensure security of our own time and place, but for our children, and their children, just as our ancestors have done for us many, many years ago,” the president said. (Rationale No. 7: for the grandkids.)

That seemed like the kind of rousing, big-picture finish on which the president might have ended day two of combat operations. But he wasn’t done. In an interview that night with ABC News, Trump hinted at another reason—self-preservation. “I got him before he got me,” he said, presumably a reference to Khamenei. The Justice Department has brought charges in two cases of alleged Iranian murder-for-hire plots, and a man allegedly backed by Iran’s Islamic Revolutionary Guard Corps is now on trial in New York, accused of a scheme to assassinate Trump. “I got him first,” the president said. (Rationale No. 8: preemptive hit.)

As the new week began, another rationale was percolating lower down the chain of command. At a Monday briefing, a combat-unit commander told officers that the war is part of God’s plan and that Trump was “anointed by Jesus to light the signal fire in Iran to cause Armageddon and mark his return to Earth,” according to a complaint by a noncommissioned officer circulated by the Military Religious Freedom Foundation, an advocacy group. (Rationale No. 9: fulfill God’s purpose.)

Elsewhere on Monday, ending Iran’s nuclear ambitions (Rationale No. 2) initially took center stage. “Crazy regimes like Iran hell-bent on prophetic Islamist delusions cannot have nuclear weapons,” Hegseth said at a briefing. Vice President Vance, in an interview with Fox News, said Trump authorized the strikes because he knew that Iran was “committed to getting on the brink of a nuclear weapon”—a notable distinction, perhaps, from actually being on that brink, or two weeks away (as the president had said).

[Read: Pete Hegseth is the Pentagon’s holy warrior]

But there was more. Secretary of State Marco Rubio, searching for an imminent threat that would have justified bypassing congressional approval, implied that Israel had forced the Pentagon’s hand because assessments showed that “if we waited for them to hit us first after they were attacked—and by someone else, Israel attacked them, they hit us first, and we waited for them to hit us—we would suffer more casualties.” House Speaker Mike Johnson said more or less the same: “Because Israel was determined to act with or without the U.S.,” the administration had a “very difficult decision” to make (Rationale No. 10: The Israelis made me do it).

That one, however, lasted barely a day. Trump, on Tuesday, said the opposite: “If anything, I might have forced Israel’s hand.” Rubio dutifully walked back his own remarks, insisting that the decision had been made separate from and prior to Israel’s. “The president systemically—made a decision to systematically destroy this terroristic capability,” Rubio said. “I was very clear in that answer.” (Rationale No. 3, it seems.) Rubio also added to some of his other previous remarks. He had warned on Monday of the “unacceptable risk” of an “entire regime” run by “radical clerics” making decisions on the basis of theology (Rationale No. 4). On Tuesday, he insisted that “our objectives remain, as they’ve been identified from the beginning.” Namely: “Iran can never have a nuclear weapon.” (Back to No. 2.) The priority of regime change had, apparently, been sublimated.

Wednesday brought us full circle: Trump ordered the strikes because he felt (yes, felt) that Iran might attack the U.S., a.k.a. the imminent threat, Rationale No. 1.

“The president had a feeling, again, based on fact, that Iran was going to strike the United States, was going to strike our assets in the region, and he made a determination to launch,” White House Press Secretary Karoline Leavitt said. (Pentagon officials said in a closed-door congressional briefing on Sunday that there is no sign that Iran was planning to attack the United States first, Reuters reported.)

Hegseth, meanwhile, included in his Wednesday briefing—among many other objectives—a reference to Rationale No. 8, assassinating the Iranian leaders alleged to have threatened the president’s life. (This, by the way, is connected to Rationale No. 5 on election interference.) “We’ve known for a long time that Iran had intentions on trying to kill President Trump and/or other U.S. officials,” he said. “And while that was not the focus of the effort by any stretch of the imagination, in fact, never raised by the president or anybody else, um, I ensured, and others ensured that those who were responsible for that were eventually part of the target list.”

Speaking at a roundtable with tech-industry leaders the same day, the president returned to Rationale No. 2, on nukes: “If we didn’t hit within two weeks, they would have had a nuclear weapon,” he said, repeating a claim for which neither the Pentagon nor the intelligence community has provided any evidence. He added a dash of change-of-government thinking (Rationale No. 4) but with the Caracas model in mind, rather than the toppling of the Iranian regime. “Venezuela worked out really great,” he said. “We have a wonderful relationship with the president.”

Those most interested in a more robust Rationale No. 4—actual regime change—needed to wait less than 24 hours. Yesterday morning, The Washington Post reported that, in calls with Kurdish minority leaders in Iran and Iraq, the president offered “extensive U.S. aircover” and other backing for Kurdish forces to take over parts of western Iran. But that needs to be considered alongside what Trump told Axios the same day: that he must be involved in the selection of Iran’s next leader, modeling that process on his experience with Venezuela. “I have to be involved in the appointment, like with Delcy in Venezuela,” he said. Later Thursday, the White House went back to relying on Rationale No. 8, posting a clip on X showing Trump saying, “I was the hunted, and now I’m the hunter.”

[Read: The glaring oversight in the U.S. war plan]

Military gains may ultimately outpace the administration’s attempts to settle on a single reason for the war. U.S. and Israeli forces report swift advances in seizing local air superiority, degrading Iran’s defensive capabilities, and killing senior Iranian figures. But the war already has come at the cost of six U.S. service members’ lives along with (by early estimates) those of more than 1,000 Iranians, and it has produced turmoil in the region and in global markets. A congressional official told our colleague Nancy A. Youssef that the Pentagon’s preliminary estimates say the war is costing taxpayers $1 billion a day.

If you can’t figure out why we are at war, maybe (according to the administration) the problem is your own inability to understand. Hegseth said Monday that the administration was “very clear-eyed” and would avoid “the foolish policies of the past” that lacked goals “tethered to actual, clear objectives.”

On Wednesday, the White House on X said much the same: “Our objectives are clear. We will not stop until they are achieved.”

A man takes a train from London to the coast. He’s visiting a town called Wulfleet. It’s small and old, the kind of place with a pub that’s been pouring pints since the Battle of Bosworth Field. He’s going to write about it for his blog. He’s excited.

He arrives, he checks in. He walks to the cute B&B he’d picked out online. And he writes it all up like any good travel blogger would: in that breezy LiveJournal style from 25 years ago, perhaps, in his case, trying a little too hard.

But as his post goes on, his language gets older. A hundred years older with each jump. The spelling changes. The grammar changes. Words you know are replaced by unfamiliar words, and his attitude gets older too, as the blogger’s voice is replaced by that of a Georgian diarist, an Elizabethan pamphleteer, a medieval chronicler.

By the middle of his post, he’s writing in what might as well be a foreign language.

But it’s not a foreign language. It’s all English.

None of the story is real: not the blogger, not the town. But the language is real, or at least realistic. I constructed the passages myself, working from what we know about how English was written in each period.1

It’s a thousand years of the English language, compressed into a single blog post.

Read it and notice where you start to struggle. Notice where you give up entirely. Then meet me on the other side and I’ll tell you what happened to the language (and the blogger).

You’re reading The Dead Language Society, where 35,000+ readers explore the hidden history of the English language. I’m Colin Gorrie: PhD linguist and your guide through 1,500 years of English being weird.

I publish every Wednesday. Paid subscribers get every issue, the full archive, and the content I’m most proud of: practical guides to reading historical texts yourself, honest takes on how language really works, and live book clubs where we read texts like Beowulf and (up next!) Sir Gawain and the Green Knight.

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2000

Well, I finally got to the town everyone has been talking about lately. Wulfleet. And let me tell you, it was not easy to get here. It’s ridiculous how close this place is to London, and yet how hard it is to get here. I took a train to some place whose name I can’t pronounce, and then from there I had to hop on a bus. The whole day was shot just getting here.

Not going to lie though: so far, it’s totally worth it.

Yes, it’s the typical English coastal town: the seagulls, the cobblestone streets, the works. But there’s something about it that just makes me want to dress up in a cape and walk around like I’m in a Gothic novel. Although, let’s be honest, do I really need an excuse to do that? :)

Everyone seems really nice here, although I did have one really weird encounter on the way to the B&B. A guy was following me for a while. It kind of freaked me out. Anyway, if you go to Wulfleet, just watch out for this one weird guy who hangs out near the bus stop. I know, real specific. But anyway, that was just a bit odd.

Speaking of which, the B&B is also… interesting. LOL. It has separate hot and cold taps and everything. I’m about to see how the “bed” portion works. I’ll update you on the “breakfast” tomorrow morning. If I can find an internet cafe around here, that is.

1900

My plans for an untroubled sleep were upset, however, when I woke with a start before dawn. The window had, it seemed, come open in the night, though I was perfectly certain I had fastened it. I sprang up from the bed to see what was the cause, but I could see nothing in the darkness — nothing, that is, that I could satisfactorily account for. I closed the window again but was entirely unable to fall asleep due to the shock. I am not, I hope, an easily frightened man, but I confess the incident left me not a little unsettled.

When dawn finally came, I went downstairs to find a well-appointed dining room in which there was laid out a modest but perfectly adequate meal. After I ate, and thanked the landlady — a respectable woman of the kind one expects to find in charge of such an establishment — I decided to take a stroll around the town. The sea air did something to revive me after the events of the previous day, not to mention the night, although a question still weighed on me. Do windows simply burst open in the night? Or was there something else afoot? I resolved to make enquiries, though of whom I was not yet certain.

1800

After spending the day wandering around the environs of the town, and, finding myself hungry, I sought out an inn, where I might buy some supper. It was not difficult to find one, and, sitting alone, I called for supper from what the publican had to offer. I confess I gave no great thought to the quality of the fare. Hunger, that great leveller, makes philosophers of us all, and renders even the meanest dish agreeable.

The place was adequately charming. The tables were covered with guttering candles, and the local rustics seemed to be amusing themselves with great jollity. Reader, I am not one of those travellers who holds himself above the common people of the places he visits. I saw fit rather to join in with their sport and we whiled away the hours together in good cheer. I found them to be as honest and amiable a company as one could wish for.

The only thing that disturbed my good humour was when I thought, for a brief moment, that I saw the man who accosted me yesterday among the crowd. But it must have been a mere fancy, for whatever I thought I saw vanished as quickly as it had appeared. I chided myself for the weakness of my nerves, and took another draught to steady them.

When, at long last, the entertainment was spent, I undertook to return to my lodgings; however, finding myself quite unable to find my way, a fact which owed something to having imbibed rather immoderately in the hours prior — and here let me caution the reader against the particular hospitality of country innkeepers, which is liberal beyond what prudence would advise — I soon found myself at the harbour’s edge.

1700

When I was firſt come to Wulfleet, I did not see the harbour, for I was weary and would ſooner go to the inn, that I might ſleep. It is a truth well known to travellers, that wearineſs of body breeds a kind of blindneſs to all things, however remarkable, and ſo it was with me. But now that I beheld the ſight of it, I marvelled. In the inky blackneſs I could see not a ſtar, nor even a ſliver of the moon. It was indeed a wonder that I did not ſtumble on my way, and periſh in a gutter, for many a man has come to his end by leſs.

Finally, with my mind much filled with reflection, I found my way through dark ſtreets to a familiar alley. This was a welcome sight, as an ill foreboding was lately come into my mind. I entertained for a moment such unmanly thoughts as are far from my cuſtom, and which I ſhould be aſhamed to ſet down here, were it not that an honeſt account requires it. I felt eſpecially that I was purſued by ſome thing unknown to me. I glanced backwards, to ſee if I might eſpy that man. But there was no one, or at least no one that I could diſcern.

At laſt, I found the doorway of the inn, as much by chance as by deſign, and retired to ſleep with a mind addled half by drink and the other half by a fear for which I could not well account. I commended myſelf to Providence, and reſolved to think no more on it.

1600

That night I was vntroubled by such euents as I had vndergone the night before, for I had barred the door ere I ſlept, and so fortified, that so no force might open it. This town of Wulfleet was paſſing ſtrange, as ſtrange I dare ſay as any place whereof Plinie wrote, or any iland discovered in the voyages of Sir Walter Raleigh. But I was bound to my taſk, and would not flinch from it. I would record the occurrents in Wulfleet, howeuer ſtrange they might ſeem, yea, though they were ſuch things as would make a leſſer man forſake his purpoſe.

But I ſoon forgot my earlier dread, for the morning brought with it ſo fair a ſight as to diſpel all feare. The people of the town had erected ouernight a market of ſuch variety and abundance as I haue not ſeen the like. Animals walked among men, and men among animals, a true maruel!

As I looked on this aſſembled throng, greatly pleaſed and not a little amazed, a man approached me. He ſtartled me, but I quickly saw he was nothing but a farmer come to hawke his wares. “Would you haue a fowl, sir?” ſaid he, “My hens are fat and luſty, and you may haue them cheap.”

I said in reply, “No, I thanke thee,” He was a churliſh fellow, rude of ſpeech and meane of aſpect, and I felt no ſhame at thouing ſuch a man as that.

1500

I went forthe among the people, and as I paſſed throughe the market and the ſtretes of the towne, euer lokyng aboute me with grete care, leſt I ſholde agayn encountre ſome peryl, thee appeared, from oute of the prees that ſame man whom I ſo dredde. And he was passyng foule was of vyſage, as it ſemed to me, more foule than ony man I had ſene in al my lyf.

He turned hym towarde me and ſayd, “Straunger, wherefore art thou come hydder?”

And I anſwerd hym nott, for I knewe nott what I ſholde ſaye, ne what answere myght ſerue me beſt in ſuche a caas.

Than hee asked me, “Was it for that thou wouldeſt ſee the Maiſter?”

And verely this name dyd me ſore affright, for who was this Maiſter wherof he ſpake? And what maner of man was he, that his very name ſholde be ſpoken wyth ſuche reuerence and drede. I wolde haue fledde but he purſued me and by myn avys he was the ſwifter, for he caught me full ſoone.

I sayd to him, “What meaneſt thou? Who is the Maiſter?”

And he sayd, “I ſhall brynge the vnto hym, and thou ſhalt ſee for thy ſelf what maner of lorde he is.”

But I wolde not, and cryed out ayenſt hym with grete noyſe, leſt he ſholde take me thyder by violence and ayenſt my wille.

1400

Bot þe man wolde me nat abandone þer, ne suffre me to passen forþ. I miȝt nat flee, for hys companiouns, of whom þer were a gret nombre, beſet me aboute, and heelden me faſt þat I ne scholde nat ascapen. And þei weren stronge menn and wel douȝti, of grymme contenaunce and fiers, and armed wiþ swerdes and wiþ knyues, so þat it were gret foly for eny man to wiþstonden hem.

So þei bounden me hond and foot and ledden me to þe one þei callede Maiſter, of whom I hadde herd so muchel and knewe so litel.

Þe sayde Maiſter, what that hee apperid bifore me, was verely a Deuill, or so me þouȝte, for neuer in al my lyf hadde I beholden so foule a creature. Hee bore a blak clok þat heng to þe grounde, and ſpake neuer a worde. Bot his countenaunce was hidous and so dredful þat my blood wexed colde to loken on hym. For he hadde nat þe visage of a man bot of a beest, wiþ þe teeþ and ſnoute of a wulf, scharpe and crueel. And his eres weren longe eres, as of a wulf, and bihynde him þer heng a gret tayl, as wulf haþ. And hys eyen schon in þe derknesse lyke brennyng coles.

“What wolden ȝe wiþ mee, ȝe heþene?” aſked I, þouȝ myn voys quaked and I hadde litel hope of eny merci.

Bot þei maden no answer, neyþer good ne yuel. Þei weren stille as stoon, and stoden about me as men þat wayte on þeir lordes commandement.

1300

Þanne after muchel tyme spak þe Maiſter, and his wordes weren colde as wintres is. His vois was as þe crying of rauenes, scharpe and schille, and al þat herde hym weren adrade and durst nat speken.

“I deme þe to þe deeþ, straunger. Here ſchaltou dyen, fer fram þi kynne and fer fram þine owen londe, and non ſchal knowen þi name, ne non schal þe biwepe.”

And I sayde to hym, wiþ what boldenesse I miȝte gaderen, “Whi fareſt þou wiþ me þus? What treſpaas haue I wrouȝt ayeins þe, þat þou demeſt me so harde a dome?”

“Swie!” quoþ he, and smot me wiþ his honde, so þat I fel to þe erþe. And þe blod ran doun from mi mouþe.

And I swied, for þe grete drede þat was icumen vpon mee was more þan I miȝte beren. Mi herte bicam as stoon, and mi lymes weren heuy as leed, and I ne miȝte namore stonden ne spoken.

Þe euele man louȝ, whan that he sawe my peine, and it was a crueel louȝter, wiþouten merci or pitee as of a man þat haþ no rewþe in his herte.

Allas! I scholde neuer hauen icumen to þis toune of Wuluesfleete! Cursed be þe dai and cursed be þe houre þat I first sette foot þerinne!

1200

Hit is muchel to seggen all þat pinunge hie on me uuroȝten, al þar sor and al þat sorȝe. Ne scal ic nefre hit forȝeten, naht uuhiles ic libbe!

Ac þer com me gret sped, and þat was a uuif, strong and stiþ! Heo com in among þe yuele men and me nerede fram heore honden.

Heo sloȝ þe heþene men þat me pyneden, sloȝ hem and fælde hem to þe grunde. Þer was blod and bale inouȝ And hie feollen leien stille, for hie ne miȝten namore stonden. Ac þe Maister, þe uuraþþe Maister, he flaȝ awei in þe deorcnesse and was iseon namore.

Ic seide hire, “Ic þanke þe, leoue uuif, for þu hauest me ineredd from dæðe and from alle mine ifoan!”

1100

Þæt ƿif me andsƿarode and cƿæð, “Ic eom Ælfgifu gehaten. Þu scalt me to ƿife nimen, þeah þe þu hit ne ƿite gyt, for hit is sƿa gedon þæt nan man ne nan ƿif ne mote heonon faren buten þurh þone dæð þæs Hlafordes.”

“Ac þær is gyt mare to donne her, forþi ƿe nabbaþ þone Hlaford ofslagenne. He is strong and sƿiðe yfel, and manige gode men he hæfð fordone on þisse stoƿe.”

“Is þæt soð?” cƿæþ ic, forþon þe ic naht ne ƿiste. “Ic ƿende þæt ic mihte heonon faren sƿa ic com.”

“Gea la,” cƿæð heo. “Hit is eall soð, and ƿyrse þonne þu ƿenst.”

1000

And þæt heo sægde wæs eall soþ. Ic ƿifode on hire, and heo ƿæs ful scyne ƿif, ƿis ond ƿælfæst. Ne gemette ic næfre ær sƿylce ƿifman. Heo ƿæs on gefeohte sƿa beald swa ænig mann, and þeah hƿæþere hire andƿlite wæs ƿynsum and fæger.

Ac ƿe naƿiht freo ne sindon, for þy þe ƿe næfre ne mihton fram Ƿulfesfleote geƿitan, nefne ƿe þone Hlaford finden and hine ofslean. Se Hlaford hæfþ þisne stede mid searocræftum gebunden, þæt nan man ne mæg hine forlætan. Ƿe sindon her sƿa fuglas on nette, swa fixas on ƿere.

And ƿe hine secaþ git, begen ætsomne, ƿer ond ƿif, þurh þa deorcan stræta þisses grimman stedes. Hƿæþere God us gefultumige!

The blog ends there. No sign-off, no “thanks for reading.” Just a few sentences in a language that most of us lost the ability to follow somewhere around the thirteenth century.

So, how far did you get?

Let me take you back through it.

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The calm after the storm (1700–2000)

Written English has been remarkably stable over the last 300 years. Spelling was standardized in the mid-1700s, and grammar has barely changed at all. This means that, if you can read Harry Potter (1997–2003), you can read Robinson Crusoe (1719), which is good news to fans of the English novel.

What has changed is the voice.

Blog post became diary entry became travel letter. The format changed much faster than the language. Compare the very first line, “Well, I finally got to the town everyone has been talking about lately” with the line from the 1800 section, “Hunger, that great leveller, makes philosophers of us all, and renders even the meanest dish agreeable.”

They’re both performances of a sort: the 2000s protagonist is performing for his blog’s audience, so the tone is chatty and personal. The 1800s protagonist, with the mind of a Georgian diarist, is performing for posterity, so he philosophizes.

The one visible change in the language itself is the appearance, in the 1700 passage, of the long s (ſ). This wasn’t a different letter, just a variant form of s used in certain positions within a word. It disappeared fully from English printing in the early 19th century, although its use was dwindling even before that, which is why it does not appear in the 1800 passage. It’s a typographic change rather than a linguistic one, but it’s the first unmistakable sign that the text is getting older.2

Slowly, then all at once (1400–1600)

This is where the ground starts to move under our feet.3

Before the mid 1700s, there was no such thing as standardized spelling. Writers spelled words as they heard them, or as they felt like spelling them, which is why the 1500s and 1600s sections look so alien, even when the words, underneath the surface, are ones you know.

For another difficulty, take the word vntroubled from the 1600 section. This is our familiar untroubled, but the u is replaced by a v, because u and v were not yet considered separate letters. They were variants of the same latter, used to represent both sounds. The convention was to write v at the beginning of words and u in the middle, which give us spelling like vnto (unto), euents (events), ouernight (overnight), and howeuer (however). It looks weird at first, but once you know the rule, the words become much more readable.

Another new arrival — or, more accurately, late departure — from the language is the letter thorn (þ), which first appears in the 1400 section. Thorn is simply th. That’s it. Wherever you see þ, read th, and the word will usually reveal itself: þe is the, þei is they, þat is that. If you’ve ever seen a pub called “Ye Olde” anything, that ye is actually þe, an attempt by early printers to write a thorn without having to make an expensive new letter.

Thorn’s companion, yogh (ȝ), is more complicated. It represents sounds that modern English spells as gh or y — so miȝt is might, ȝe is ye. The reasons for this are a story unto themselves.

But the most interesting change in this period isn’t a letter. Rather, it’s a pronoun. Notice the moment in the 1600 section where our blogger meets a farmer and says, “No, I thanke thee.” Then he adds, “I felt no ſhame at thouing ſuch a man as that.”

Thouing. To thou someone, or to use thou when talking to them, was, by the 1600s, a deliberate social statement. Thou was the old singular form of you; you was originally the plural. Over the centuries, you came to be used as a polite singular, much as French uses vous. Gradually, you took over entirely. By Shakespeare’s time (1564–1616), thou survived in two main contexts: intimacy (as in prayer) and insult. Our blogger is being a little rude here. He’s looking down on a man he considers beneath him, and his language gives him a way of making his feelings perfectly clear.

Over the wall (1000–1300)

Somewhere in this section — and if you’re like most readers, it happened around 1300 or 1200 — the language crossed a boundary. Up to this point, comprehension felt like it was dropping gradually, but now it’s fallen off a cliff. In one section, you could get by by squinting and guessing; in the next you were utterly lost. You have hit the wall.4

There are two reasons for this. The first is vocabulary. As you move backwards in time, the French and Latin loanwords that make up an enormous proportion of the Modern English vocabulary grow fewer and fewer. When you pass 1250, they drop off almost altogether. Where a modern writer would say he underwent torture, a 1200-era writer must say that he suffered pinunge instead.5

The farther back you go, the more the familiar Latinate layer of English is stripped away, revealing the Germanic core underneath: a language that looks to modern eyes more like German or Icelandic than anything we’d call English.

The second reason for the difficulty is grammar. Old English (450–1100) was an inflected language: it used endings on nouns, adjectives, and verbs to mark their grammatical roles in a sentence, much as Latin or modern German do. Alongside these endings came a greater freedom in word order, which makes sense given that the endings told you who was doing what to whom.

English lost most of these endings over the course of the period linguists call Middle English (1100–1450), and it tightened its word order as if to compensate. When you look at these final sections, if you can make out the words, you will see the effects of this freer word order. For example, in 1200 we read monige gode men he hæfð fordone ‘many good men he has destroyed’, where we’d expect a Modern English order more like and he has destroyed many good men.

To make matters worse, a few unfamiliar letters also appear: wynn (ƿ) is simply w, eth (ð) means the same as thorn (þ) — both represent th, and ash (æ) represents the vowel in cat and hat.6:

All of these factors combined likely made it difficult, if not impossible, to follow the plot. So let me tell you what happened. In the 1400 section, the blogger was seized. He was dragged before a creature they called the Master, and the Master was no man. He had the teeth and snout of a wolf, as well as a wolf’s long ears and great tail. His eyes glowed like burning coals. Wulfleet was once Wulfesfleot ‘the Bay of the Wolf.’

In the 1300 section, the Master condemned our hero to death. In the 1200 section, a woman appeared and killed his captor. The Master, however, fled into the darkness. In the 1100 section, the woman revealed her name: Ælfgifu ‘gift of the elves.’ She told the blogger — can we still call him that in 1100? — they would marry, and she shares the terrible truth about Wulfleet: no one leaves until the Master is dead.

In the 1000 section, they are married. She is, he writes, as bold as any man in battle, and yet fair of face. But they are not free. Together, through the dark streets of Wulfleet, they hunt the Master still.

The English in which I write this paragraph is not the English of fifty years ago, and it will not be the English of fifty years in the future.

Go back far enough, and English writing becomes unrecognisable. Go forward far enough and the same thing will happen, though none of us will be around to notice.

Our poor blogger didn’t notice either, even as he and his language travelled back in time through the centuries. He just kept writing even as he was carried off to somewhere he couldn’t come back from. Some say that, far away in Wulfleet, he’s writing still.

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The birthday-party invitation said “siblings welcome,” which means you can bring your 11-month-old son while your husband is out of town. You arrive a little disheveled and a little late. Your 5-year-old daughter rushes into the living room, and you make your way to the kitchen, wearing your son in a sling. You find a few moms around a table arrayed with plates of fruit, hummus, celery sticks, and carrots—no gluten, no nuts, no Red 40. These parents care about avoiding pesticides, screen time, and processed foods, and you do too.

It’s a classic kids’ party: Tears and lemonade are spilled; mud and cake get smeared into the rug; confetti balloons are popped one by one, showering elated children in rainbow-paper flakes. Sunbeams through the windows illuminate floating dust motes—and, imperceptibly, microdroplets of mucus carrying the measles virus, expelled from an infected but asymptomatic child who is hopping and laughing among the others. Your daughter breathes that same air, inhaling the virus directly into her respiratory tract.

The infected aerosolized droplets will linger in the air for hours, which is partly why measles is among the most contagious diseases in the world. The virus infects roughly 90 percent of unvaccinated people exposed to it; the infected can then, in turn, infect a dozen to several hundred people each, depending on where they are and what they’re doing. Breakthrough cases are possible among the vaccinated, but they tend to be rare, relatively mild, and less likely to spread. A single dose of the MMR vaccine is 93 percent effective at preventing infection; two doses are 97 percent effective. Among the unvaccinated, one in five people infected with measles in the United States will require hospitalization, and roughly two out of every 1,000 infected children will die of complications, regardless of medical care.

Your daughter behaves normally over the next week while the virus slowly spreads inside her, infecting immune cells that carry it to the lymph nodes, where it replicates and spreads at a rapid pace. Your daughter is at school cutting alphabet shapes out of paper when the virus enters her bloodstream. But she doesn’t feel anything until she seems to come down with a cold—dry cough, runny nose, itchy and watery eyes—about a week after the party, because the virus has multiplied and descended upon her lungs, kidneys, tonsils, and spleen, down to the marrow of her bones. When she starts running a fever, your mind turns to the logistics of taking off work while she’s home from school. You’ve witnessed enough colds as a mother to not be worried about this one. You feel some confidence in your instincts when it comes to your child’s health, and you’ve grown skeptical of medical interventions. It’s why you and your husband decided to wait to vaccinate your kids, though you’re a little conflicted about it. You’re not an extremist. You’re open to new information. You can always change your mind, you reason. You’re just weighing the evidence.

Ten days out from the party, your daughter’s cold has worsened. Her throat is sore, her appetite is low, and she’s running a fever that sometimes ticks up to 104. Colds can be rough. You plant her on the couch with a blanket and put Bluey on the TV while she drifts in and out of sleep. You coax her to eat by offering ice cream, which she says feels good on her throat. She’s a tough kid, but you can tell she’s miserable—there are circles under her eyes as she complains of a headache, then grimaces when she coughs. You can feel with a tender touch that the glands in her neck are swollen and uncomfortable. Her fever still hasn’t dropped. After a few days, you experience the first tug of serious concern. On the phone, your mom suggests that it might be COVID, or maybe the flu. Push fluids, she says, and keep an eye on it. You put your daughter to sleep in your bed, in case she needs you in the night.

[Read: His daughter was America’s first measles death in a decade]

The next morning, you lay your hand on her forehead, and the heat of her skin sends a ripple of unease through you. The measles virus is attacking the cells that line her lungs and suppressing her immune system, rendering her vulnerable to secondary infections. You step away to feed the baby and put him in clean clothes, but then rush back when you hear her calling you in a strained, croaking voice, her vocal cords swollen and thick with mucus. You find her lying in bed with her hand over her eyelids and tear tracks on her temples. She asks you to close the curtains because the sunlight is hurting her eyes—the virus has triggered a case of conjunctivitis. In all of the colds you’ve nursed her through, she has never complained of pain triggered by light. When you rouse her to give her Tylenol, you see that the whites of her eyes are reddened, and the bases of her eyelashes sticky. You carefully clean her eye area with a damp paper towel, kiss her nose, then leave her to sleep it off.

While the kids are napping, you tap a list of your daughter’s symptoms into Google and find a slew of diseases that more or less match up, because fevers, coughs, and sore throats are common to many illnesses. You post about it to the parents’ group, where a few moms with ill kids offer solidarity, and others commiserate over similar episodes with their own children. One woman says it’s time to call the doctor. You’ve had friction with your pediatrician over vaccinations, but this mom may be right. Later that day, when your little girl is curled up on the couch with a cold chocolate-milk protein shake, you go to take her temperature and find that her face is dotted with a spotty red rash descending from her hairline. The virus has infected capillaries in her skin, which typically happens three to five days after the symptoms start, but you don’t know that. It doesn’t hurt, she says, though it’s itchy. Her fever remains high and unrelenting. You pull out your phone and type chicken pox symptoms into your browser, hoping that you’ve found a viable culprit. It sort of fits, so you hold off on calling the doctor.

But her condition does not improve over the next couple of days. Her cough wracks her whole body, rounding her delicate bird shoulders. She does not sleep well. And as you lift up her pajama top to check her rash one morning, you see that her breathing is labored, shadows pooling between her ribs when she sucks in air. You suffer an icy moment of realization: This is a medical crisis. What you will learn later is that the tiny air sacs inside her lungs have become breeding grounds for the virus, and the inflammation generated by her immune response is inhibiting oxygen from reaching her bloodstream. You don’t want to worry your daughter, so you try to sound calm when you call the pediatrician and describe her symptoms at a rapid clip. The receptionist responds gently, types swiftly, and then pauses. Are your children vaccinated? she asks. Her tone is flat and inscrutable, but you detect an undercurrent of judgment. You wince and tell her the truth. No, you say, no vaccines. She puts you on hold. While you wait, you take your son out of his high chair and wipe his runny nose with his bib.

The receptionist is back. She asks if you can be at the office within the hour. In an even, professional voice, she gives you a number to call as soon as you arrive, but tells you to stay in your car. The doctor, she says, will come to you.

You’re there in 30 minutes, unshowered and wearing sweatpants, with your daughter bundled up and shivering in her pajamas and your son fussing in his car seat. You call the office. From the car, you cannot see the sign on the pediatrician’s office door instructing patients with a list of symptoms like your daughter’s not to come inside. Flashes of the pandemic play back as you see the pediatrician and two nurses approaching in the rearview mirror wearing N95 masks. It hits you: This is not the flu. This is not chicken pox. This is serious.

You twist around in the front seat to watch the pediatrician as she leans into your car and begins her exam, asking you questions about symptoms and timing. A nurse takes swabs from the nose and throat, which will be sent for testing by the local public-health authority, then clips a pulse oximeter onto your daughter’s fingertip. The doctor leans in to lay the cold diaphragm of her stethoscope against your daughter’s back. The doctor tells her to breathe. You tell her she’s doing a great job, and reach back to pet her knee. The doctor hears crackling with every breath your daughter takes, as air moves through the fluid trapped in her lungs. The oximeter reveals that her blood is only 90 percent saturated with oxygen, well below the healthy range of 95 to 100 percent. The pediatrician tells you to drive directly to the hospital. Your daughter is in pain and bewildered and afraid, but you tell her everything is okay; you’re just going to see a different doctor. Your son is fussing in his car seat. You try to keep your voice even, though your heart is pounding.

While you drive a little too fast to the emergency room, the pediatrician’s office calls the hospital warning them that there is a suspected measles patient on the way, and then places a mandatory call to the public-health authority notifying them of your daughter’s condition. Once you arrive, things happen quickly. Because measles is what researchers call a high-consequence infectious disease, health-care professionals undertake a series of strict protocols to limit its spread. You and your daughter are fitted with masks before you are brought in through a side door to avoid contaminating the waiting room, and then herded into an isolated negative-pressure room designed to prevent the aerosolized virus from traveling into the hall. After hospital workers whisk your daughter away for an emergency X-ray, they will shut down the areas of the radiology department for six hours to carry out decontamination measures, a thorough process protracted by the virus’s capacity to cling to walls and linger in the air. While your daughter gets her scan, you try to soothe your son, whose forehead begins to feel worryingly hot to you.

Your daughter looks so small in her hospital bed, her face fitted with an oxygen mask. Nurses collect blood and urine; you hold the cup as she shivers on the toilet, then stroke her hair as the needle spears her vein. When you’ve regained some composure a couple of hours later, a doctor comes to speak with you. This is the first time anyone has used the word measles. The doctor tells you that your daughter has pneumonia, a complication arising in roughly 6 percent of measles cases, though some researchers suspect that the actual rate may be higher. There is no cure for viral pneumonia from measles, but the hospital will provide supportive care to treat the symptoms, including her scalding fever and rash. The doctor doesn’t tell you then that pneumonia is the most common cause of death in measles patients. You will learn that later on.

The swabs taken by the pediatrician test positive for measles, and your child’s case becomes a data point in an outbreak. Each measles patient can infect a dozen or more unvaccinated people, and cases in your community are multiplying rapidly. A public-health official comes to gather information for contact tracing, and asks you to think of everyone your child has interacted with in the past couple of weeks. You think of her class at school, the grocery store, the car wash where you wait indoors, the birthday party.

Articles will soon appear in the local newspaper asking people who may have visited the post office or Target or the indoor playground on various days during various time frames to call the public-health office. Your child’s school will send out emails asking that parents keep unvaccinated children at home for the next three weeks, the virus’s maximum incubation period. As the outbreak spreads, local pediatricians will offer the MMR vaccine to children younger than a year old, because unvaccinated infants are especially vulnerable to the disease. The exponential growth in measles cases in the area attracts media attention, recriminations, and questions about blame.

Not that you notice. You practically live in the intensive-care unit as your daughter slowly recovers. When they discharge her a week later, they send instructions for at-home care, including hydration, decent air humidity, and plenty of rest. The disease will leave her with a lingering cough and occasional wheezing, and it will take months for her lungs to fully heal. She will fall behind in school and need tutoring to catch up, but all of these complications will seem trivial after you’ve come so close to something so dark that you can barely contemplate it. In the meantime, and until her rash heals, your daughter’s doctor insists that she remain under quarantine at home—along with your son.

Given your son’s fever, runny nose, and evident discomfort, you feel a grim sense of resignation when his measles test comes back positive. You are, however, alarmed when you discover there’s nothing his doctors can do about it. Had he been seen by a doctor within 72 hours of his first exposure, they could have given him a prophylactic dose of the MMR vaccine to protect him from infection. But it’s too late for that now. And you couldn’t have known then, anyway—when he was exposed, your daughter wasn’t symptomatic yet.

You feel uneasy caring for your son at home, having witnessed what the infection did to your daughter. But he is medically stable for now, and isolating him at home will limit the spread of the disease. You anxiously wonder whether you’ll know when his needs turn critical, particularly because he is too young to tell you how he feels. He cries inconsolably, unlike your daughter, and sometimes screams. After his rash appears, you notice when he wakes from a nap that pus has drained from his ear onto his crib sheets. You will learn later that an opportunistic bacterial infection has taken advantage of your son’s suppressed immunity by setting up in his middle ear, causing inflammation and fluid buildup to burst his eardrum. You call the pediatrician’s office, and they patch you through to the doctor. You wait for her in the same spot in the parking lot as last time. She diagnoses your son with a severe ear infection and prescribes antibiotics. On a superstitious level, you think this means nothing else bad can happen.

But within a few days, your son’s fever will spike as high as 105 degrees. The virus will break through his underdeveloped blood-brain barrier and begin attacking his brain matter directly, leading to primary measles encephalitis. The condition is rare among older children but more common in infants, who are also more likely to die from measles. You will panic and call an ambulance when he slumps over unconscious on the floor, and another swarm of doctors and nurses will descend upon your child and whisk him away deep into the building while you trail behind as closely as you can. Like your daughter, your son will need supportive care, but he will also need close monitoring of the pressure inside his skull. While your husband stays home with your daughter, you keep vigil at the hospital for as long as you’re allowed, sometimes sleeping in the car to avoid missing any time squeezing his little hand. Days pass, then a week, two weeks. The nurses are kind. There are now several other children in the same hospital unit suffering from measles complications, some of them tethered to ventilators.

Somehow, your son recovers well enough for you to take him home. He has lost some of his hearing, but the doctors say that he could make a full recovery in a matter of months. It is hard to describe the gift this is, the relief you feel. Most children infected with measles will survive the virus, but 30 percent of cases lead to complications, and it is nearly impossible to predict which patients will be affected.

[Katherine J. Wu: The only thing that will turn measles back]

Your children seem so fragile as they recover over the next year, but then the four of you are back to your usual adventures. For roughly eight years, you will believe that your family made it through this crisis without suffering a tragedy. You marvel at your good fortune, and feel a rush of gratitude the day your daughter returns to school and life resumes its normal rhythm. But years later, when your baby is in fourth grade, he will begin struggling with subjects he had once mastered. His teachers will ask to speak with you about how he is suddenly acting out in uncharacteristic ways.

You will not think of his measles infection when he begins suffering muscle spasms in his arms and hands, nor when his pediatrician recommends that you see a neurologist. You realize you have entered a new nightmare when nurses affix metal electrodes to your son’s scalp with a cold conductive paste to perform an electroencephalogram to measure his brain waves. As the neurologist examines the results, she will note the presence of Radermecker complexes: periodic spikes in electrical activity that correlate with the muscle spasms that have become disruptive. She will order a test of his cerebrospinal fluid to confirm what she suspects: The measles never really left your son. Instead, the virus mutated and spread through the synapses between his brain cells, steadily damaging brain tissue long after he seemed to recover.

You will be sitting down in an exam room when the neurologist delivers the diagnosis of subacute sclerosing panencephalitis, a rare measles complication that leads to irreversible degeneration of the brain. There are treatments but no cure, the neurologist will tell you. She tells you that your son will continue to lose brain function as time passes, resulting in seizures, severe dementia, and, in a matter of two or three years, death. You look at your son, the glasses you picked out with him, the haircut he chose from the wall at the barbershop, the beating heart you gave him. You imagine your husband’s face when you break the news, the talks you will have with your daughter, your mother, your in-laws—though there is no way to prepare for what is coming. And you know that you, too, will never recover.

This story is based on extensive reporting and interviews with physicians, including those who have cared directly for patients with measles.