You do not have to cite a source for knowledge that's generally known among your readers or is a well-known fact.

Question

Quizplus · Accepted Answer

It is not necessary to cite a source for information that is considered common knowledge or is widely accepted as a fact among your target audience. However, what constitutes common knowledge may vary depending on the audience, discipline, and context, so it is still important to make sure you're not assuming too much and that your readers can reasonably be expected to know the information you're presenting as fact.

You Do Not Have to Cite a Source for Knowledge