Clinical reasoning and the new "non-" nosology

Although seemingly odd, the designations prefixed with "non-" have become a familiar feature of clinical terminology. A common structure of these designations is the partition of a single clinical category into two contrasting ones. Despite the similar "non-" designations, the partitions can have four different functions: dividing one disease into two, aggregating multiple diseases, distinguishing etiologic uncertainty, and negating "legitimate" disease. The "non-" terminology may seem peculiar, but it is based on clinically pertinent distinctions and similarities in disease, reflecting prudent clinical reasoning.