 | This is an information page. It is not one of Wikipedia's policies or guidelines; rather, its purpose is to explain certain aspects of Wikipedia's norms, customs, technicalities, or practices. It may reflect differing levels of consensus and vetting. |
A frequent justification in casual conversation is that a certain fact is "common knowledge". It often turns out that most people don't actually share this knowledge. Even claims that are widely believed often turn out to be anywhere from only mostly true to the complete opposite of what is actually the case.
Wikipedia editors are strongly encouraged to find reliable sources to support their edits, and to cite them. Citing sources when your edit is challenged by another editor is Wikipedia policy, and any unsourced edits may be removed. For more information, see Wikipedia:No original research and Wikipedia:Verifiability.
There are some claims that many Wikipedians find acceptable to report as fact, without citing any outside sources. This guideline seeks to define when it's a bad idea to do that.