Classicly

There is no hard and fast line between the normal and the abnormal person, and indeed a very real difficulty exists in even defining a normal person. If we take our definition of normal as being “average or conforming to type or standard,” then the majority of people are normal. If, on the other hand, we take its other meaning, that of “performing the proper functions,” then there are few people approaching the normal under modern civilized conditions. A tendency to undue irritability or depression is a mild and very common form of abnormality. Hysterias, obsessions, and unreasonable fears are greater abnormalities, and fortunately of less frequent occurrence, while certain forms of insanity are still greater deviations from the normal.