On July 21, 2007, my daughter Maggie and I fought our way into a crowded Dublin bookstore and bought not one but two copies of Harry Potter and the Deathly Hallows, which was published worldwide that day. Over the next 36 hours, we raced each other through the pages to learn the fate of Harry Potter, his Hogwarts friends, and the world of wizardry in general.

In the last full chapter, the boy wizard at last defeats the evil Voldemort. An epilogue set 19 years later shows that Harry has achieved an ambiguous adult normality, with a happy marriage, a station wagon, and three children who are off to Hogwarts themselves. The series’ final sentence refers to the scar Harry has carried since the murder of his parents when he was a baby: “The scar had not pained Harry for nineteen years,” it reads. “All was well."

Millions of young people drew from Deathly Hallows a message every young person longs to hear: that they can triumph over the outsize fears of adolescence, and that beyond them await full and normal lives.

Let’s imagine, though, that the World’s Greatest Literary Critic—call him Gilderoy Lockhart—reviews the book in the World’s Most Important Literary Journal. Lockhart notes what he considers an important grammatical fact in the next-to-last sentence: It is written only in the past perfect. It does not say, “The scar had not pained Harry for nineteen years, did not pain him now, and would not pain him in the future.” That means, Lockhart explains, that the scar has begun to hurt at that moment—and will continue to hurt forever. He points to other places in the series where Rowling has written that things “did not” hurt or “would not” hurt. Affirming that the scar “had not pained Harry” means denying that it “is not” painful or “will not” be painful. “All was well” means that all had been well up to that moment, but was not well any more and would never be well again.

“Rowling knows how to use the simple past or the simple future tense when she chooses,” Lockhart writes. “She did not use it. Using one tense excludes all other tenses.”

The book’s “correct” message to the young is this: There is no hope. The world is a dark plain of Dursleys and Malfoys, under the eternal shadow of You-Know-Who.

Suppose now that J.K. Rowling contests this reading; the choice of past perfect in context encompasses past, present, and future, she might say. Lockhart dismisses her evidence as self-interested and dishonest. Other critics argue that one sentence, taken in isolation, cannot determine the meaning of an epic series sprawling over more than 3,000 pages. These critics, too, Lockhart says, are deceitful or incompetent. His reading is the only correct one.

In literary circles (where I once alas dwelt), Lockhart’s review would be ascribed to spite and envy, the kind of destructive criticisms in which some critics engage to prove that they matter.

But in fact it would be worse than spiteful. It would be wrong.

This kind of erroneous reading is at the center of King v. Burwell, the latest challenge to the Affordable Care Act. King, which will be argued in front of the Supreme Court on March 4, involves the interaction of four short sections of the 1,200-page Act. These sections are crucial to its goal of providing health insurance to millions of American families who could not afford it before.

The first of these is Section 1501, the “individual mandate” requiring heads of households to obtain health insurance or pay a tax. The second is Section 1311(b)(1), which instructs states to set up “American Health Benefit Exchanges” so that their residents can find suitable policies. The third is Section 1401, which directs the Internal Revenue Service to provide tax credits and subsidies for millions of low- and middle-income taxpayers for policies purchased on “an Exchange established by the State under 1311.” The fourth, Section 1321, recognizes that the federal government can’t order states to do anything (the Supreme Court has made that clear); thus if for any reason a state chooses not to set up an exchange (or tries to, like Oregon, and fails), the federal government is required to “establish and operate such Exchange within the State.”

Despite predictions of disaster by its opponents, the system has begun to work relatively well. According to a report this week by the non-partisan Congressional Budget Office, the ACA in 2014 provided insurance for 12 million people who otherwise would be uninsured; that number will rise to 19 million by the end of 2015. Estimates of the cost of the ACA, meanwhile, are lower than initially projected, according to the CBO.

But conservative lawyers have vowed to destroy Obamacare. In King, they argue that one phrase (not even a complete sentence) should doom the entire 1,200-page Act. They claim that when 1401 says “established by the state” it means—can only mean—one thing. Consumers whose states don’t establish exchanges—and who thus must get their coverage through a federal exchange set up for the state—don’t get their subsidies.

If the Supreme Court accepts that reading, the loss of subsidies and credits will price coverage out of reach for middle-income consumers in 34 states. As many as 9 million people will lose their insurance; the interstate insurance market will be set in turmoil; the entire ACA system may collapse.

That collapse is what the challengers hope for.

Their argument is that the statute doesn’t say “established by the state or by the federal government.” Does it need to? A federal exchange is “such” exchange, meaning the same thing as a state exchange. Let’s look at dictionaries endorsed by Justice Antonin Scalia. Black’s Law Dictionary defines “such” as meaning “of this kind or that kind . . . That or those; having just been mentioned.” The Oxford English Dictionary defines it as, “[o]f the character, degree, or extent described, referred to, or implied in what has been said.” The American Heritage Dictionary of the English Language says simply, “[o]f this kind.” Webster’s New World College Dictionary says, “of the same or a similar kind.” The New Oxford American Dictionary says, “of the type previously mentioned.” The Shorter Oxford English Dictionary says, “of the kind, degree, or category previously specified or implied contextually.”

A federal exchange functions precisely the same way as a state exchange, and the statute treats them identically. Like Rowling’s closing assurance that “all was well,” which plainly indicates a happy ending, the phrase “established by the state,” in context, clearly incorporates the federal exchanges. That reading makes perfect sense; it accords with what we know about the purpose of the Act, and with the professed intentions of its authors; and it reads the Act as a whole rather than as a lifeless jumble of half-sentences.

The federal judiciary is split between two theories of interpretation. One school argues that statutes are human constructs, tools by which “we the people” govern ourselves. Courts are co-equal branches of government, and their job is to aid self-government, not frustrate it; they should read statutes in reasonable harmony with their text and their evident purpose, using all available tools of interpretation. One of those tools is “legislative history”—statements about the bill made by congressional committees and legislators during passage. As Judge Robert Katzmann of the Second Circuit writes in his new book, Judging Statutes, actual legislators use legislative history to communicate their intentions to courts and administrative agencies. A judge using these tools would, I think, easily read “such exchange” as meaning that state or federal exchanges are identical in operation and effect.

A second theory, however, comes from parts of the legal right. It insists that neither contemporary statements nor legislative history should make any difference. All that count are individual words and a big dictionary of the judge’s choice.

Of course, even the more sophisticated proponents of this “textualism” recognize how absurd it is to read phrases in isolation. At oral argument this month in Texas Dept. of Housing and Community Affairs v. Inclusive Communities Project, Inc., Justice Scalia explained that “when we look at a provision of law, we look at the entire provision of law, including later amendments. We try to make sense of the law as a whole.”

Wise words; but judges are as human as the rest of us; when they see the chance to read their own political leanings into a high-stakes, partisan dispute, the temptation to ignore “the law as a whole” must be all but irresistible.

I cling to the hope, however, that some of them will resist it.

A contrary decision would be malicious and spiteful.

Even worse, it would be wrong.