Reforming the country’s health-care system is so difficult because when the system works, it works very well. Reformers must avoid tampering with the quality of care as they try to improve access and lower costs. With that in mind, one of the primary questions to reform has been, how does the country make changes to some parts of the system without affecting others?

The truth is that it can’t, not entirely. But it shouldn’t want to, either. Add the 37 million uninsured Americans to the medical rolls without making broad changes in the way care is delivered to those currently with coverage and disaster certainly will follow. Providing access to medical care to all Americans means recasting the best parts of the current system to fit a model that far more people can use.

Beyond preventive care and, for instance, optional surgery, medical care ultimately is unique among services: Unlike shopping for a car and eventually deciding that mass transit will suffice, a person with a broken leg can’t decide whether to have medical care. Unlike choosing among foods that have similar nutritional values, one surgical procedure can’t be substituted for another.

The slow realization that medical care must be a right of citizenship will produce changes in the way the health-care system is shaped. Greater access means more preventive care and more primary care: The pressure will be placed on medical schools to produce more general practitioners and fewer specialists. A health-insurance system that covers everyone will be forced to define a basic level of coverage. Task forces such as the one led by First Lady Hillary Rodham Clinton will have to set limits on what illnesses will be covered, as the state of Oregon has tried to do with its plan.

As consumers, Americans must demand a health-care system that offers enough choice among medical servers to encourage efficiencies while maintaining a single-payer system for a basic level of care. Access to such a system must be guaranteed. Until now, health care in the United States has served as a fixer of medical problems, rather than as a system that helped maintain health. It is far cheaper to keep people healthy than to cure their illnesses.

With these health-care rights will come responsibilities to use the system well — preventive care over emergency procedures — and pressure on all people to take care of themselves — the same sort of pressure produced in reaction to abuses of the welfare system. And abusers of a reformed health-care system will be far more costly to those paying for it.

But as Sen. William Cohen points out in his column on today’s Op-ed page, access for all is the first step: Having a high-quality system is useless to people who can’t afford to gain entry to it. “Without question, the innovation and investment in research by drug companies have given us relief from literally hundreds of afflictions and provide hope that one day we can find the cure for such devastating diseases as Alzheimer’s, AIDS and cancer,” the senator writes. “Yet their research is in vain if these medicines are beyond the financial reach of consumers. Buying a prescription drug is not an elective decision. For most people, it is an absolute necessity.”

Changes in the health-care system cannot be achieved a little piece at a time because each piece — coverage, cost, quality, type of care, etc. — is directly dependent on every other. As a nation with great skill and great exclusivity in its health services, Americans must demand such a large-scale overhaul.