However, I believe that the application of DSM criteria to the borderline areas I have been discussing is limited by two basic weaknesses. The first is that no subjective checklist of a patient's history and complaints can infallibly separate clinical syndromes that qualify as disorders from various kinds of human discomfort of lesser intensity. What is needed and what is still lacking is some kind of biological marker, such as tissue alterations or a serologic or imaging abnormality, that can distinguish, say, a clinical depression from a state of unhappiness. Such biological markers are available in other branches of medicine but not in psychiatry, except to a very limited degree. It is also true that most people who have depression, clinical or not, have other problems and concerns that affect their feelings and will influence the criteria by which they are diagnosed.