Common knowledge is NOT considered plagiarism. According to Rozakis, " 'common knowledge' is defined as the information an educated person is expected to know...Common knowledge falls into many categories. Here are some examples of common knowledge that you don't have to document:
Rozakis, Laurie E., Ph.D. The Complete Idiot's Guide to Research Methods. New York: Alpha Books, 2004. Print.
A secondary source is a source you are citing that cited an ORIGINAL source of information. In this case, you would cite the original source and include the phrase, "as cited in (secondary source)..."
As stated by the University of Michigan's Research Guide, "collaboration is sometimes unacceptable when a student works with another or others on a project and then submits written work which is represented explicitly or implicitly as the student's own work.
Equally unacceptable is submitting a group project in which you did little or none of the work yet you take the credit for the work done by others within your group."
You must also keep in mind that when instructor's say an essay or paper should be written individually, if you collaborate with someone else on the writing process, you are participating in unethical collaboration and potentially plagiarizing.
When copying someone else's words exactly as they are written, you must make sure to use direct quotations. A direct quotation uses quotations marks (" ") around the words or phrases that are being copied. This type of citation indicates that the words you are using are someone else's and not your own.
The other type of citation is indirect quotations. An indirect quotation is either a paraphrase or a summary of the original text. A paraphrase or summary condenses the original text and typically employs your own words to express the author's meaning or purpose behind the original text.
If the author said it better than you ever could, you should use DIRECT quotations. Many times, the effect of the words is better carried by the author's voice rather than your own. If you are trying to demonstrate what you understood from the text or if your paper has too many direct quotations, then you should use a paraphrase or a summary.
Regardless or which you use, you must be sure to cite your source!
Any unique, or original, thought of your own does not need to be quoted...
BUT
If you reuse content from a paper you have already written and submitted for another class, you DO have to quote yourself.