When you use exact language from a source, you need to show that it is a quotation.
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 CMS-3a). To omit the quotation marks is to claim—falsely—that the language is your own. Such an omission is plagiarism even if you have cited the source.
original source
For many Southerners it was psychologically impossible to see a black man bearing arms as anything but an incipient slave uprising complete with arson, murder, pillage, and rapine.
—Dudley Taylor Cornish, The Sable Arm, p. 158
plagiarism
According to Civil War historian Dudley Taylor Cornish, for many Southerners it was psychologically impossible to see a black man bearing arms as anything but an incipient slave uprising complete with arson, murder, pillage, and rapine.2
borrowed language in quotation marks
According to Civil War historian Dudley Taylor Cornish, “For many Southerners it was psychologically impossible to see a black man bearing arms as anything but an incipient slave uprising complete with arson, murder, pillage, and rapine.”2
note: Long quotations are set off from the text by indenting and do not need quotation marks (see the example in CMS-3a).