Common knowledge refers to information or facts that are found in many places and are likely to be known by the general public.
For example: George Washington was the first president of the United States..
This is a widely known fact. It is not necessary to cite a source for this fact.
However, it is necessary to cite the sources of facts that are not generally known or ideas that interpret facts.
For example: At the 1892 NAWSA Convention, Elizabeth Cady Stanton delivered her “Solitude of Self” speech, the fullest expression of her feminist philosophy.
The idea that Cady Stanton’s speech represented the “fullest expression of her feminist philosophy” is an evaluation of her speech, not a fact, and therefore the source should be cited. When in doubt as to whether something is widely known, it is safer to cite the source.
Paraphrasing is the act of using someone else’s ideas, but putting them in your own words. Even though you use your own words when you paraphrase, it is still necessary to acknowledge and cite the original source. You aren't citing the words, you're acknowledging the use of the ideas.
A quotation is the use of someone else’s words verbatim. When you put someone else’s words in your work, you must surround the exact quote in quotation marks and cite the original source using an appropriate citation format.
The realm embracing property rights that belong to the community at large, are unprotected by copyright or patent, and are subject to appropriation by anyone (definition from Merriam Webster dictionary). You must cite the ideas in public domain works in the same way that you would cite copyrighted works.
Some artists and writers voluntarily place their work into the public domain upon creation, but most public domain works are such because the copyright on them has expired. If there isn't a clear statement of it being in the public domain, it should be assumed that a work is copyrighted.
