section_path: Areas of study/Periods
section_name: Periods
paragraph_text: Periods
  
  Historical study often focuses on events and developments that occur in particular blocks of time. Historians give these periods of time names in order to allow "organising ideas and classificatory generalisations" to be used by historians. The names given to a period can vary with geographical location, as can the dates of the beginning and end of a particular period. Centuries and decades are commonly used periods and the time they represent depends on the dating system used. Most periods are constructed retrospectively and so reflect value judgments made about the past. The way periods are constructed and the names given to them can affect the way they are viewed and studied.