History (from Greek ?st???a - historia, meaning "inquiry, knowledge acquired by investigation") is the discovery, collection, organization, and presentation of information about past events. History can also mean the period of time after writing was invented. Scholars who write about history are called historians. It is a field of research which uses a narrative to examine and analyse the sequence of events, and it sometimes attempts to investigate objectively the patterns of cause and effect that determine events. Historians debate the nature of history and its usefulness. This includes discussing the study of the discipline as an end in itself and as a way of providing "perspective" on the problems of the present. The stories common to a particular culture, but not supported by external sources (such as the legends surrounding King Arthur) are usually classified as cultural heritage rather than the "disinterested investigation" needed by the discipline of history. Events of the past prior to written record are considered prehistory.