Research that consists of collecting and organizing material from existing sources within the provisions of this and other content policies is fundamental to writing an encyclopedia. Best practice is to research the most reliable sources on the topic and summarize what they say in your own words, with each statement in the article attributable to a source that makes that statement explicitly. Source material should be carefully summarized or rephrased without changing its meaning or implication. Take care not to go beyond what is expressed in the sources, or to use them in ways inconsistent with the intention of the source, such as using material out of context. In short, stick to the sources.
If no reliable third-party sources can be found on a topic, Wikipedia should not have an article about it. If you discover something new, Wikipedia is not the place to announce such a discovery.
Any material that is challenged or likely to be challenged must be supported by a reliable source. Material for which no reliable source can be found is considered original research. The only way you can show your edit is not original research is to cite a reliable published source that contains the same material. Even with well-sourced material, if you use it out of context, or to reach or imply a conclusion not directly and explicitly supported by the source, you are engaging in original research; see below.
In general, the most reliable sources are:
- Peer-reviewed journals
- Books published by university presses
- University-level textbooks
- Magazines, journals, and books published by respected publishing houses
- Mainstream newspapers
As a rule of thumb, the more people engaged in checking facts, analyzing legal issues, and scrutinizing the writing, the more reliable the publication. Self-published material, whether on paper or online, is generally not regarded as reliable, but see self-published sources for exceptions.
Information in an article must be verifiable in the references cited. In general, article statements should not rely on unclear or inconsistent passages, or on passing comments. Passages open to multiple interpretations should be precisely cited or avoided. A summary of extensive discussion should reflect the conclusions of the source. Drawing conclusions not evident in the reference is original research regardless of the type of source. It is important that references be cited in context and on topic.
Primary, secondary and tertiary sources
Wikipedia articles should be based on reliable, published secondary sources and, to a lesser extent, on tertiary sources and primary sources. Secondary or tertiary sources are needed to establish the topic's notability and to avoid novel interpretations of primary sources. All analyses and interpretive or synthetic claims about primary sources must be referenced to a secondary or tertiary source, and must not be an original analysis of the primary-source material by Wikipedia editors.
Appropriate sourcing can be a complicated issue, and these are general rules. Deciding whether primary, secondary or tertiary sources are appropriate in any given instance is a matter of good editorial judgment and common sense, and should be discussed on article talk pages. A source may be considered primary for one statement but secondary for a different one, and sources can contain both primary and secondary source material for the same statement. For the purposes of this policy, primary, secondary and tertiary sources are defined as follows:[b]
- Primary sources are original materials that are close to an event, and are often accounts written by people who are directly involved. They offer an insider's view of an event, a period of history, a work of art, a political decision, and so on. Primary sources may or may not be independent or third-party sources. An account of a traffic incident written by a witness is a primary source of information about the event; similarly, a scientific paper documenting a new experiment conducted by the author is a primary source on the outcome of that experiment. Historical documents such as diaries are primary sources.[c]
- Policy: Unless restricted by another policy, primary sources that have been reputably published may be used in Wikipedia, but only with care, because it is easy to misuse them.[d] Any interpretation of primary source material requires a reliable secondary source for that interpretation. A primary source may only be used on Wikipedia to make straightforward, descriptive statements of facts that can be verified by any educated person with access to the primary source but without further, specialized knowledge. For example, an article about a novel may cite passages to describe the plot, but any interpretation needs a secondary source.
- Do not analyze, evaluate, interpret, or synthesize material found in a primary source yourself; instead, refer to reliable secondary sources that do so.
- Do not base an entire article on primary sources, and be cautious about basing large passages on them.
- A secondary source provides an author's own thinking based on primary sources, generally at least one step removed from an event. It contains an author's analysis, evaluation, interpretation, or synthesis of the facts, evidence, concepts, and ideas taken from primary sources. Secondary sources are not necessarily independent or third-party sources. They rely on primary sources for their material, making analytic or evaluative claims about them.[e] For example, a review article that analyzes research papers in a field is a secondary source for the research.[f] Whether a source is primary or secondary depends on context. A book by a military historian about the Second World War might be a secondary source about the war, but where it includes details of the author's own war experiences, it would be a primary source about those experiences. A book review too can be an opinion, summary or scholarly review.[g]
- Policy: Wikipedia articles usually rely on material from reliable secondary sources. Articles may make an analytic, evaluative, interpretive, or synthetic claim only if that has been published by a reliable secondary source.
- Tertiary sources are publications such as encyclopedias and other compendia that summarize primary and secondary sources. Wikipedia is a tertiary source.[h] Many introductory undergraduate-level textbooks are regarded as tertiary sources because they sum up multiple secondary sources.
- Policy: Reliable tertiary sources can be helpful in providing broad summaries of topics that involve many primary and secondary sources, and may be helpful in evaluating due weight, especially when primary or secondary sources contradict each other. Some tertiary sources are more reliable than others, and within any given tertiary source, some entries may be more reliable than others. Wikipedia articles may not be used as tertiary sources in other Wikipedia articles, but are sometimes used as primary sources in articles about Wikipedia itself (see Category:Wikipedia and Category:WikiProject Wikipedia articles).