Normal

Normal regularly functions as an approximate synonym for “healthy.” The word emerged in writing about medicine and health at the start of the nineteenth century and has played a prominent role there ever since. But even as the term continues to hold a central place in the field, its precise meaning can appear vague and elusive. A useful way to bring this ambiguity under control is to identify the series of meanings, some of them inconsistent to the point of contradiction, that the word has taken on in the two centuries or so since it first appeared.