Plagiarism: where to draw the line

Both teachers and students run into problems identifying plagiarism. When citing someone else, you must either use quotation marks or significantly alter the phrasing of the idea. The problem is with that word, significantly. What does that mean?

Here's an original paragraph followed by a number of hypothetical uses by students extracted from the middle of an essay. The extremes are quite easy to identify, but where do you draw the line between legitimate use and copying?

Original

"There is a good deal of evidence that job opportunities in the United States are polarizing, and that, as a result, the country's future as a middle-class society is in jeopardy. What the decline of the middle class would mean to the country can only be guessed at, but it presumably would be unwelcome to the millions of parents who hope that their children can move up the economic ladder; to American business, which needs a middle class to consume its products; and to everyone who is concerned about fairness and social harmony."

by Bob Kuttner, The Atlantic Monthly, July 1983

Sample A (limited lexical substitution)

Kuttner (1983) argues that there is a lot of evidence that job chances in the United States are polarizing, so the country's future as a middle-class society may be hurt. What the decrease of the middle class would mean to the country is unclear, but it probably would be unwelcome to the millions of adults who hope that their children can move up economically; to American business, which needs a middle class to buy its products; and to everyone who is worried about fairness and social harmony.

Sample B (increasing lexical substitution; limited deletion)

Kuttner (1983) argues that there is a lot of support for the idea that jobs in the United States are splitting into high-paying and low-paying jobs, so its future as a middle-class country may be hurt. What the decrease of the middle class would mean is unclear, but it probably would not be welcome to American adults who want their children to have a good job; to companies, which need a middle class to buy what they make; and to people who want justice and no social problems.

Sample C (extensive lexical substitution; limited deletion; limited structural change)

Kuttner (1983) argues that jobs in the United States are splitting into high-paying and low-paying jobs. Consequently, the country may lose its middle-class. The result of this is unclear, but most American adults who want their children to have a good job would be unhappy about it, as would companies, who would lose customers, and people who want justice and no social problems.

Sample D (extensive lexical and structural changes, limited quotation)

Claiming that there is good reason to believe that the difference between high- and low-paying U.S. jobs is increasing, Kuttner (1983) argues, “the country's future as a middle-class society is in jeopardy.” We can only imagine what effect this will have, but concerned groups would likely include parents, worried about their children’s future careers, businesses, worried about loss of customers, and others worried about loss of social equity.

Sample E (extensive deletion and lexical substitution; some structural change)

Kuttner (1983) argues that America is losing its middle class and claims that although we don’t know what the effect of this will be, it seems likely to be negative for everyone from business to low-income parents.