But that's only one of the issues the justices will rule on. If they strike down the insurance mandate, they must also decide whether the rest of the 2,700-page law must go - that is, whether the mandate is "severable" from the legislation.
There is much in those thousands of pages that already directly affects many people. Patients with major illnesses such as cancer no longer face lifetime caps on their coverage. Children with chronic illnesses such as asthma and diabetes are guaranteed coverage regardless of how sick they are. And young adults up to the age of 26 can be covered under their parents' policies if they can't get insurance elsewhere.
The law contains other provisions that affect many people indirectly. It creates a new system for judging and improving the quality of hospitals to prevent more medical errors. It implements new public health and prevention programs to make screening, immunizations, and physical exams available without co-payments. And it permits cheaper, generic versions of advanced drugs.
The law doesn't explicitly say whether the individual insurance mandate is severable from these other provisions. In such situations, courts try to determine what Congress intended. That is less a matter of legal doctrine than a judgment call.
The 26 attorneys general who brought the suit the Supreme Court will consider want the entire law thrown out. What purpose would that serve? The mandate is a crucial element of the law, one that would reshape the individual insurance market. But it isn't everything.
Few of the law's other provisions are controversial, either legally or politically. Indeed, polls show many of them are wildly popular. And if they were discarded, many people would suffer. Coverage limits could be reinstated for patients who have already run up large bills, sick children could lose their policies, and young people could find themselves once again uninsured.
If the justices decide to strike down the mandate, leaving the other provisions in the balance, they must take particular care to be in touch with the world around them - a world where health-care reform has already done a lot to improve people's lives.
Robert I. Field is a professor of law at the Drexel University Earle Mack School of Law and a professor of health management and policy at the Drexel School of Public Health, as well as a regular contributor to the Inquirer's "Checkup" blog. He can be reached at firstname.lastname@example.org.