The word “depression” has come to be used in psychiatry to denote both a syndrome (or symptom:sign cluster) and one or more of the symptoms commonly occurring in this cluster. This attribution of two meanings to one term has led to considerable confusion. Thus it is often claimed that depression may be present in almost any mental illness. This statement may be true in the sense that the mood of depression may occur in almost any mental illness; but it cannot be true in the sense that the depressive syndrome may enter into almost any mental illness, since the term depressive syndrome has already, at least by implication, been used to denote a particular symptom:sign cluster which differentiates it from all other symptom:sign clusters. To deny this would be to deny the original principles of division.