Citation, Documentation of Sources
Q. I am still trying to grasp the whole idea of footnotes using CMOS. Do I put a footnote after everything that I use out of a book even if it’s not a quote? For example, I am writing a paper on Thomas Jefferson and in one of the books I’m using it states that he had six sisters and a younger brother. Do I need to cite that in a footnote?
A. Not necessarily, if you believe that the information about Jefferson’s siblings is generally known and mentioned in many sources. You should footnote information that you borrow from someone else that isn’t common knowledge, whether you quote it or not; and if any of the information is disputed (for instance, if some sources say that Jefferson had seven sisters), it’s a good idea to footnote the version that supports your statement. Even if you don’t footnote general information about Jefferson in your text, you should list the source you learned it from in your bibliography.
The idea of footnotes is to acknowledge where you got your information, both in order to give credit to the researchers who did the work and in order to tell your readers where they can find the information. Everyone knows that George Washington was the first president, so even if you read it somewhere, there are so many sources that say so that it doesn’t make sense to give credit to a particular one.
It’s not always clear whether something should be cited or not, so until you develop some confidence, be generous in your citations, without being silly.