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 | This page in a nutshell: Use retrospective sources over contemporary sources whenever possible. |
Contemporary sources, or real-time sources, include all sources about an event that are produced as new information comes out. They most commonly take the form of news reports, and they are contrasted with retrospective sources, which analyze an event from a historical perspective. Contemporary sources are rarely ideal, and they should be avoided when possible.
Contemporary sources and real-time coverage of an event provide the facts of an event, but they do not place it in context or determine its broader significance. News coverage and other contemporary sources are often routine, and even exceptional coverage doesn't necessarily indicate that the event should be mentioned in an article. An event that seems significant at the time can end up being insignificant in the overall scope of the article. Since it is difficult to measure significance and due weight using contemporary sources, using them to write content causes editors to make their own conclusions about significance and give the content disproportionate weight.
Instead, articles should use retrospective sources that were written later, such as books about the subject, journal articles that analyze it, or even newspaper articles that provide a long-form retrospective analysis of the subject. Tertiary sources such as encyclopedias are also useful for determining how much weight to give individual events as part of a broader article. Real-time sources about an event are primary sources for the event itself. They can be primary sources or a secondary sources for people and places mentioned in the source, depending on how the source is used. Use of primary sources should follow the Wikipedia guideline on using primary sources.
The key is not to wait a certain number of months or years, but to compare contemporary and retrospective sources. Contemporary sources can still be written well after an event initially began or took place. If a crime is committed, real-time sources about the trial are still contemporary, even if the trial goes on for years. Likewise, if a disaster occurs, sources about the resulting investigation are still real-time sources because they entail publication of new information as it develops.