It is likely not to change our understanding, and may be an impediment to better identification of subjects and treatments. An example of an essentialist identification is Hepatitis B or C. Here, there is no

link to symptoms or signs – just to the cause. The doctor’s skill then consists in identifying the causal disease and prescribing the appropriate treatment. This concept of disease is not yet applicable Inhibitors,research,lifescience,medical in a broad sense to psychiatry, because much less is known, and Trichostatin A molecular weight causation is likely to be multifactorial. However, as evidence of causation develops, an essentialist mentality can move the field forward. The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) points out that “there is no assumption that each category of mental disorder is a completely discrete entity with absolute boundaries dividing it from other Inhibitors,research,lifescience,medical mental disorders or from no mental disorder” (p 21),10 but the mere fact that a diagnostic concept is listed, official,

and provided with a precise definition makes Inhibitors,research,lifescience,medical it appear robust and specific. Definitions are stated to become codified and reified without an examination of the fundamental validity. Robins and Guze11 proposed formal criteria for establishing the validity of psychiatric diagnoses; however few of the entities in DSM meet these criteria. As Kendell and others have pointed out, it is likely that the concept of a nominalist description of disease in the psychiatric context as a distinct entity may not be relevant.6 One of the hallmarks for symptom- and course-based identification is to demonstrate points of nonoverlap between similar syndromes.9,11 The points of rarity between psychiatric diseases defined Inhibitors,research,lifescience,medical in a nominalist tradition are not as distinct as one would like. On the other hand, an essentialist classification

may be very relevant. We have recently noted a Inhibitors,research,lifescience,medical system for defining a condition as a disease. Criteria for defining disease The first and obvious criterion is that the condition should be one that leads to a risk for adverse outcomes – either mortality or functional impairment.12 The second is where an identifiable characteristic genetic or environmental factor or pathology can be Oxalosuccinic acid clearly defined. This characteristic should separate the entity from similar entities, in terms of at least one of the following criteria: Clinical symptoms Course and outcome Familial pattern Treatment response. The differentiation should be clinically significant. Clinical significance may have to be adjudicated by collective groups. Trie failure to separate may change over time as additional information is developed, and may go through a stage where the characteristic is considered as a subentity.12,13 Is the time right to ask whether there are potential essentialist conditions relevant to depression? I think it is, and I would like to introduce the notion of two such categories.