Nosology (from the Greek νόσος, nosos, "disease" + λόγος "logos")'s a branch of medicine that deals with classification of diseases. Diseases may be classified by etiology (cause), pathogenesis (mechanism by which the disease's caused), or by symptom(s). Alternatively, diseases may be classified according to the organ system involved, though this's often complicated since many diseases affect more than one organ. A chief difficulty in nosology's… (More on Nosology)