Pathology is a significant component of the causal study of disease and a major field in modern medical practice and diagnosis. The term pathology itself may be used broadly to refer to the study of disease in general, incorporating a wide range of bioscience research fields and medical practices, or more narrowly to describe work within the contemporary medical field of "general pathology," which includes a number of distinct but inter-related medical specialties which diagnose disease mostly through the analysis of tissue, cell, and body fluid samples. Used as a count noun, "a pathology" (plural, "pathologies") can also refer to the predicted or actual progression of particular diseases (as in the statement "the many different forms of cancer have diverse pathologies"), and the affix path is sometimes used to indicate a state of disease in cases of both physical ailment (as in cardiomyopathy) and psychological conditions (such as psychopathy). A physician practicing pathology is called a pathologist.
As a field of general inquiry and research, pathology addresses four components of disease: cause/etiology, mechanisms of development (pathogenesis), structural alterations of cells (morphologic changes), and the consequences of changes (clinical manifestations). In common medical practice, general pathology is mostly concerned with analyzing known clinical abnormalities that are markers or precursors for both infectious and non-infectious disease and is conducted by experts in one of two major specialties, anatomical pathology and clinical pathology. Further divisions in specialty exist on the basis of the involved sample types (comparing, for example, cytopathology, hematopathology, and histopathology), organs (as in renal pathology), and physiological systems (oral pathology), as well as on the basis of the focus of the examination (as with forensic pathology).