Originally developed by Roman Catholics to deal with problems of surgery (prior to the discovery of antisepsis and anesthesia), the distinction was used to determine whether a patient's refusal of treatment should be classified as suicide. Refusal of "ordinary" means of treatment was considered suicide, while refusal of "extraordinary" means was not. Likewise, families and physicians did not commit homicide or violate obligations to patients if they only withheld or terminated "extraordinary" means of treatment.

II. G K Kelly's Description

Ordinary means are all medicines, treatments, and operations, which offer a reasonable hope of benefit and which can be obtained and used without excessive expense, pain, or other inconvenience. Extraordinary means are all medicines, treatments, and operations, which cannot be obtained or used without excessive expense, pain or other inconvenience, or which if used, would not offer a reasonable hope of benefit.
—G Kelly, "The Duty to Preserve Life," Theological Studies., 12, Dec. '51, p. 550.

III. Definitions and distinctions

Ordinary = obligatory
Ordinary does not = usual

Extraordinary = optional
Extraordinary does not = unusual

The "usual/unusual" distinction builds on what is customary in medical practice, which in turn is connected to the "professional practice" standard. But what is customary in medical practice is merely relevant to moral judgments and cannot always be construed as morally decisive. For example, it may be usual medical practice to treat disease "x" in manner "y," but whether this usual practice should be repeated for a particular patient depends on the patient's condition as a whole and not merely on what is usual treatment for disease "x." Ethics is not reducible to consensus or to traditional codes, oaths, and practices-as useful as these may be in many professional contexts.

IV. Two criteria for obligation

Thus there can be identified two criteria for a therapy to be obligatory or required. It must (a) offer a reasonable prospect of benefit, and (b) not involve excessive expense, pain or inconvenience.

V. Meaning is moral, not descriptive

Ordinary/extraordinary means are determined not by classifying the technology but by considering its impact on the patient and his/her overall condition, thus avoiding the "technological imperative."

Consequently, a procedure is judged ordinary in a normative sense if its effects on the patient provide proportionately more benefits than burdens. On the other hand, a treatment is extraordinary in a moral sense if the evaluation produces a contrary conclusion. Thus these terms are best seen as the conclusion of a process of evaluation rather than as a classification of procedure. Thus the meaning of the terms is moral, not descriptive.

VI. Conclusion

If one accepts that the central and overarching goal of clinical medicine is to enhance the qualitative relation between the patient's condition and the pursuit of life's goods, then all things being equal, when medicine can intervene to ameliorate the quality of the relation between the patient's condition and the pursuit of life's goals, then such an intervention can be considered a benefit to the patient and is in his/her best interests.