The following information types do NOT require a citation (see also the link to the University of Wisconsin Writing Center above):

• Your own words, ideas, conclusions, and original research.
• Common knowledge: facts you can find in multiple sources.  These might include: birth and death dates; birth and death locations; and the dates of broadly known historical events.
• Common knowledge: things we can easily observe.  These might include:  leaves turn color in the autumn; the Arno River runs through Florence, Italy; and the dining hall is crowded at lunch time.
• Common knowledge: common sayings.  These might include: a rolling stone gathers no moss; in for a penny, in for a pound; hit the hay; and when it rains, it pours.