When you use exact language from a source, you need to show that it is a quotation.
Quotation marks for direct quotations: P5-a
Your research paper represents your ideas in conversation with the ideas in your sources. To be fair and responsible, you must acknowledge your debt to the writers of those sources. If you don’t, you commit plagiarism, a serious academic offense. (See also R2-c.)
In general, these three acts are considered plagiarism: (1) failing to cite quotations and borrowed ideas, (2) failing to enclose borrowed language in quotation marks, and (3) failing to put summaries and paraphrases in your own words. Definitions of plagiarism may vary; it’s a good idea to find out how your school defines academic dishonesty.