An anachronism (from the Greek ἀνά ana, 'against' and χρόνος khronos, 'time') is a chronological inconsistency in some arrangement, especially a juxtaposition of people, events, objects, language terms and customs from different time periods. The most common type of anachronism is an object misplaced in time, but it may be a verbal expression, a technology, a philosophical idea, a musical style, a material, a plant or animal, a custom, or anything else associated with a particular period that is placed outside its proper temporal domain. An anachronism may be either intentional or unintentional. Intentional anachronisms may be introduced into a literary or artistic work to help a contemporary audience engage more readily with a historical period. Anachronism can also be used intentionally for purposes of rhetoric, propaganda, comedy, or shock. Unintentional anachronisms may occur when a writer, artist, or performer is unaware of differences in technology, terminology and language, customs and attitudes, or even fashions between different historical periods and eras. A parachronism (from the Greek παρά, "on the side", and χρόνος, "time") is anything that appears in a time period in which it is not normally found (though not sufficiently out of place as to be impossible). This may be an object, idiomatic expression, technology, philosophical idea, musical style, material, custom, or anything else so closely bound to a particular time period as to seem strange when encountered in a later era. They may be objects or ideas that were once common but are now considered rare or inappropriate. They can take the form of obsolete technology or outdated fashion or idioms. A prochronism (from the Greek πρό, "before", and χρόνος, "time") is an impossible anachronism which occurs when an object or idea has not yet been invented when the situation takes place, and therefore could not have possibly existed at the time.