We cite ANY TIME we use an outside source. An outside source is anything that is not your own idea.
Here are the two steps for citing outside sources in MLA style:
Common knowledge is information that your average reader doesn't have to look up and you DON'T have to cite or reference.
For example:
If you are in a biology class and writing for your instructor or students with more knowledge of biology than the average reader then these facts probably don't need to be cited
If your audience are all of a similar cultural or national group, you don't need to cite information common to shared history.
You always need to cite and reference:
For example:
When in doubt, cite your sources!
Whenever you have a reference at the end of your paper, you need at least one intext citation to go with it. Every intext citation should point to a reference at the end of your paper.
References and Intext Citations Go Together Like Peas and Carrots.
Your intext citation contains the first word(s) of your reference so the reader can find it easily.
For optimal decomposition, experts believe you should aim for a carbon to nitrogen ratio of 30:1 (Johnson 29).
Johnson, Lorraine. "Compost Happens: The Secret to Making Quick Gardener's Gold Instead of a Slow, Stinking Mess Requires, Like Everything Else, Balance." Canadian Gardening, vol. 12, no. 1, Feb, 2001, pp. 28-33. ProQuest, https://proxy154.nclive.org/login?