What identifies a case in this area?
Plagiarism is committed when one author uses another work (typically the work of another author) without permission, credit, or acknowledgment. Plagiarism takes different forms, from literal copying to paraphrasing the work of another. In judging whether an author has plagiarized, the following definitions may be instructive:
Literal copying is reproducing a work word for word, in whole or in part, without permission and acknowledgment of the original source. Literal copying is obvious plagiarism and is easy to detect by comparing the papers in question.
Substantial copying is reproducing a substantial part of a work, without permission and acknowledgment of the original source. In determining what is “substantial,” both the quantity and the quality of the copied content are relevant. Quality refers to the relative value of the copied text in proportion to the work as a whole. Where the essence of a work has been reproduced, even if only a small part of the original work, plagiarism may have occurred. For example, a relatively short extract from a piece of music may be instantly recognizable and may constitute a substantial part.
In addition to judging the quantity and quality of the copied content, you should consider the following question: Has the author benefited from the skill and judgment of the original author? The degree to which the answer to this question is “yes” will indicate whether substantial copying has taken place.
Copying may take place without reproducing the exact words used in the original work, i.e. without literal or substantial copying. This type of copying is known as paraphrasing, and it can be the most difficult type of plagiarism to detect.
To determine whether unacceptable paraphrasing has occurred, you should apply a test similar to that for substantial copying: Look at the quantity and quality of what has been taken and also at whether the second author has benefited from the skill and judgment of the first author. If it seems clear, on a balance of probabilities, that the second author has taken without permission or acknowledgment all or a substantial part of the original work and used it to create a second work, albeit expressed in different words, then such use amounts to plagiarism.