To indicate that you are using a source’s exact phrases or sentences, you must enclose them in quotation marks unless they have been set off from the text by indenting (see MLA-3a). To omit the quotation marks is to claim—falsely—that the language is your own, as in the example below. Such an omission is plagiarism even if you have cited the source.
original source
Although these policies may have a positive impact on human health, they open the door to excessive government control over food, which could restrict dietary choices, interfere with cultural, ethnic, and religious traditions, and exacerbate socioeconomic inequalities.
—David Resnik, “Trans Fat Bans and Human Freedom,” p. 31
plagiarism
Bioethicist David Resnik points out that government policies to ban trans fats may have a positive impact on human health, but they open the door to excessive government control over food, which could restrict dietary choices and interfere with cultural, ethnic, and religious traditions (31).
borrowed language in quotation marks
Bioethicist David Resnik emphasizes that government policies to ban trans fats, despite their potential to make our society healthier, “open the door to excessive government control over food, which could restrict dietary choices, interfere with cultural, ethnic, and religious traditions, and exacerbate socioeconomic inequalities” (31).