Depression is another important example. Severe, clear-cut depression, especially if combined with manic phases, is an unequivocal disorder that conforms satisfactorily to the medical model. However, less severe episodes of depressive affect cannot always be accurately distinguished from ordinary human unhappiness or "the blues," states of mind that do not justify a diagnostic label. In the words of the author of a recent book about the experience of depression (4), "if depression is an illness that affects as much as 25 percent of the people in the world, can it, in fact, be an illness?"