How to define music has long been the subject of debate; philosophers, musicians, and, more recently, various, social, and natural scientists have argued about what constitutes music. The definition has varied through history, in different regions, and within societies. Definitions vary as music, like art, is a subjectively perceived phenomenon. Its definition has been tackled by philosophers of art, lexicographers, composers, music critics, musicians, or semiologists, linguists, sociologists, and neurologists. Music may be defined according to various criteria including organization, pleasantness, intent, social construction, perceptual processes and engagement, universal aspects or family resemblances, and through contrast or negative definition.