legal, and practical concerns beyond third-party payment, the issue is most identified with controversies about what health insurance plans should cover. For some years, insurers, clinicians, and health services researchers have argued about what care is medically necessary or appropriate and who should make such judgments. That argument is taking on new intensity and significance as proposals for health care reform call for a package of basic benefits to be defined and used more or less uniformly by public and private health insurance plans.

Adjectives such as "necessary" and "basic" are quite common in everyday language, but they also have certain specialized uses that may be inconsistent with each other and with what might be termed ordinary usage. The result is a sizable opportunity for misunderstanding and failed communication. What follows is a brief review of definitions and perspectives intended to illustrate this point.

Dictionaries⁹ describe something that is necessary as being "of an inevitable nature," "compulsory," "absolutely needed," "required,'' "essential," "indispensable," "vital for the fulfillment of a need"; it is something "that cannot be done without" or that is "determined by force of nature or circumstance." Appropriate means what is "especially suitable or compatible, fitting," "suitable or fitting for a particular purpose; proper," or "specifically fitted or suitable." What is indicated may be "necessary" or, less strongly, "advisable" or "suitable." That which is basic is "fundamental," "essential," "constituting the starting point," "primary," or "of lowest rank." A minimum is the "least quantity assignable, admissible, or possible" or the "least amount attainable, allowable, or usual."

The term medical necessity appears to have arisen several decades ago as newly developing health plans sought to limit payment or reimbursement to only that care that was medically necessary for the diagnosis and treatment of a condition, illness, or injury.¹⁰ However, not all insurance programs employ the term in contracts and elsewhere, and not all programs that use the term actually define it. When definitions are provided, they vary considerably (Helvestine, 1989).