Diagnosis of depression is clinical. Self reporting via standardized questions is an ordinary medical method. "Where does it hurt?" "When did it start?" "Is there a history of heart disease in your family?." "When did your baby start crying?"

'Illness' provides a framework for recognition and treatment. The book with the guidelines is medical not religious. The guidelines are guided by empiricism not revelation. Treatments are selected based on statistics rather than authority. There's general agreement that the book's content might be wrong. There's a process for changing it and the expectation that it will be rewritten.

Criteria for diagnosing depression in the DSM include behavioral "thinking of suicide," physically measurable "weight loss," and general well being "fatigue." The suicide criterion is more conducive to empirical confirmation than "headache" or "joint pain."