How should DSM criteria relate to the disorders they are designed to assess? To address this question empirically, the author examines how well DSM-5 symptomatic criteria for major depression capture the descriptions of clinical depression in the post-Kraepelin Western psychiatric tradition as described in textbooks published between 1900 and 1960. Eighteen symptoms and signs of depression were described, 10 of which are covered by the DSM criteria for major depression or melancholia. For two symptoms (mood and cognitive content), DSM criteria are considerably narrower than those described in the textbooks. Five symptoms and signs (changes in volition/motivation, slowing of speech, anxiety, other physical symptoms, and depersonalization/derealization) are not present in the DSM criteria. Compared with the DSM criteria, these authors gave greater emphasis to cognitive, physical, and psychomotor changes, and less to neurovegetative symptoms. These results suggest that important features of major depression are not captured by DSM criteria. This is unproblematic as long as DSM criteria are understood to index rather than constitute psychiatric disorders. However, since DSM-III, our field has moved toward a reification of DSM that implicitly assumes that psychiatric disorders are actually just the DSM criteria. That is, we have taken an index of something for the thing itself. For example, good diagnostic criteria should be succinct and require minimal inference, but some critical clinical phenomena are subtle, difficult to assess, and experienced in widely varying ways. This conceptual error has contributed to the impoverishment of psychopathology and has affected our research, clinical work, and teaching in some undesirable ways.