History (from Greek á¼±στορία, historia, meaning 'inquiry; knowledge acquired by investigation') is the study of the past. Events occurring before the invention of writing systems are considered prehistory. "History" is an umbrella term that relates to past events as well as the memory, discovery, collection, organization, presentation, and interpretation of information about these events. Scholars who focus on history are called historians. The historian's role is to place the past in context, using sources from moments and events, and filling in the gaps to the best of their ability. Written documents are not the only sources historians use to develop their understanding of the past. They also use material objects, oral accounts, ecological markers, art, and artifacts as historical sources. History also includes the academic discipline which uses narrative to describe, examine, question, and analyze a sequence of past events, investigate the patterns of cause and effect that are related to them. Historians seek to understand and represent the past through narratives. They often debate which narrative best explains an event, as well as the significance of different causes and effects. Historians also debate the nature of history and its usefulness by discussing the study of the discipline as an end in itself and as a way of providing "perspective" on the problems of the present.