Oral arguments at the U.S. Supreme Court, or any appellate court, are just one part of the process of arriving at a ruling. Briefs have been filed. Discussion follows. After their extraordinary six hours this week jousting with attorneys in the case challenging the constitutionality of the Affordable Care Act, the justices would do well to dwell on the uniqueness of the health-care market. There resides the persuasive argument for upholding the individual mandate and thus the entire law enacted by Congress in 2010.

Listen to their questioning, and Justices Antonin Scalia and Samuel Alito appear convinced that the mandate, a requirement that all Americans (with few exceptions) purchase health coverage, represents a step too far, exceeding the broad congressional authority to regulate interstate commerce. Yet, near the end of the argument, Justice Anthony Kennedy did appear open to the unique qualities of health care. His could be the deciding vote in preserving a framework, flawed as it is, for improving access and affordability in health care.

What is unique?

Everyone eventually participates in the market. Everyone receives care when they need it. Most, knowing they may not be able to afford the expense of care, purchase health insurance. Yet many do not buy coverage, often because they don’t think they will need it or because the price is too high. They amount to “free riders,” receiving care but without the money or a policy to cover the cost. So the expense is picked up across the system, roughly $40 billion a year, adding about $1,000 annually to the premium of a typical household.

This cost-shifting distorts the market. If most of us receive coverage through our employer, those seeking individual policies, often with pre-existing conditions, encounter exorbitant prices for insurance. Congress looked to make repairs. It did so by requiring insurers to provide coverage and by mandating that everyone get insurance, increasing the risk pool and spreading more evenly the cost.

Opponents of the mandate argue the government should not be allowed to force someone into commerce. Yet, clearly, by not having coverage, or self-insuring, in effect, millions of Americans have a profound impact on a health-care market totaling 17 percent of the national economy.

Kennedy and other justices wondered: What would stop an empowered Congress from mandating the purchase of broccoli or cell phones? The broccoli market doesn’t have the same features as health care. Everyone doesn’t enter the broccoli market. When you refrain from buying broccoli, you aren’t shifting the cost to others.

Congress faced a particular, and long-standing, problem. It could have taken other paths to a remedy, which argues for letting the rest of the law stand if the court opts to toss the mandate. In choosing to require the purchase of insurance, lawmakers acted easily within their authority, the boundary defined by a unique market.