Paradigm traces to a Greek verb meaning "to show," and has been used in English to mean "example" or "pattern" since the 15th century. Some debate exists, however, about what kind of example qualifies as a paradigm. Some people say it's a typical example, while others insist it must be an outstanding or perfect example. The scientific community has added to the confusion by using it to mean "a theoretical framework," a sense popularized by American scientist Thomas S. Kuhn in the second edition of his influential book The Structure of Scientific Revolutions, published in 1970. In that work, Kuhn admitted that he had used paradigm in 22 different ways. Some usage commentators now advise avoiding the term entirely on the grounds that it is overused.