When a popular professor was accused of plagiarizing content for a speech and books he authored, Arizona State University had to confront uncomfortable questions about what is simply careless copying and what is outright intellectual theft.

Is it plagiarism, for example, when a speech contains many exact words from a published article but the speaker never credits the source? What about lifting entire passages from Wikipedia and using them, unattributed, in a book?

Those were among the allegations from faculty members that led to the investigation of history professor Matthew Whitaker's works. Whitaker denied plagiarizing. After reviewing the claims, an ASU committee concluded last month that Whitaker had not committed "systematic or substantial plagiarism," but it added that there are "reasons for concern about occasional carelessness in the use of materials and sources and some less than optimal detail in attribution."...