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To the Editor: We appreciate the comments of our fifteen colleagues who commented on the “definitions” article (1–3). Before responding to the substance, we first would like to assert that the definition of epilepsy expressed eis open to revision, but it was carefully considered. The process of forming the definition spanned three years of an ILAE subcommittee, and the definitions passed through three levels of nonanonymous review (subcommittee, Commission on Diagnostic Methods, ILAE Executive Committee), and then anonymous review in Epilepsia, done with a guest editor to maintain anonymity, since the first author also is an Epilepsia editor. In response to the point of Dr. Gomez-Alonso and associates (3), publication of an article in a peer-reviewed journal, such as Epilepsia, is not and should not be automatic, simply because it represents a consensus of an official ILAE body. Webster's dictionary defines the word “definition” as “a statement expressing the essential nature of something” (4). Some definitions are “mechanistic” and others “operational.” We favored the former, but are sympathetic to the desire of some to use operational definitions for specific purposes, because the two are not mutually exclusive. Some studies may choose to continue to use the “two spontaneous seizures” definition for ease of application. A mechanistic definition does not require intrinsically that it be easily applied; rather, the key is that it captures the essence. What then is the essential nature of epilepsy? In 1888, Gowers declared that “epilepsy is applied to a disease in which there are convulsions of a certain type, or sudden impairment of consciousness, but in which the convulsions are not directly due to active organic brain disease…” (5). No requirement for two seizures was expressed. As pointed out by Beghi et al. (1), the “two seizure” requirement came later. How clear is this commonly recognized definition? The older definition typically is taken to require two “unprovoked” seizures, but the meaning of “unprovoked” is elusive. Does provocation include sleep deprivation, stress, hormonal cycles, and many other immeasurable factors? All seizures are provoked by some internal or external stimulus, whether or not we recognize the provocation. We submit that the existing definition is flawed and ambiguous, although in a familiar way that brings comfort to some epidemiologists. The subcommittee and reviewers believe that the essence of epilepsy is an exhibited seizure, in conjunction with an enduring predisposition to generate further epileptic seizures. For example, most practitioners would choose to treat an individual with an astrocytoma with anti-seizure medications after a single seizure. As such, it seems inaccurate to call this treatment for an acute symptomatic seizure, since the acute seizure already has happened. In fact, the treatment is to reduce the relatively high likelihood of a future seizure. We assert that this circumstance refers to a condition that should be called epilepsy. Conversely, circumstances can be imagined with two seizures, widely separated in time and due to different causes, not correctly labeled as epilepsy. The inclusion of associated conditions was discussed extensively in the committee. Whether such conditions are so universal as to be an intrinsic part of the definition can continue to be debated. Our definition should not affect the approach to a first seizure. In fact, physicians usually try to ascertain whether there is an enduring epileptogenic abnormality before making a diagnosis. The conditions mentioned by Beghi et al. (1), such as recurrent febrile seizures or a seizure within a week of a stroke, do not meet our definition of epilepsy. The subcommittee did not feel justified, at current levels of knowledge, in putting numerical criteria on the “enduring predisposition,” but if we had, it would have been calibrated to a level (e.g., more than a 50% lifetime risk) that would have rendered the prevalence of epilepsy not so different from those that exist today. We agree with Dr. Ahmed (3) that clarification of the meaning of enduring predisposition,” including expert input from epidemiologists, would be welcome. In conclusion, the easiest definition is not always the best. In American baseball, rule changes, which have happened about twelve times since the days when Gowers was alive (6), have driven baseball statisticians to despair, but most of the changes have made for a better game. We are sorry that Beghi et al. (1) believe that the new definitions, “do not advance the field in any way”; however, the stimulus to discuss, debate, refine and revise such definitions may in fact advance our understanding and the clarity of our thinking.