 In normal science, the scientist’s activity consists in solving puzzles rather than testing fundamental theories. In puzzle-solving, current theory is accepted, and the puzzle is indeed defined in its terms. In Kuhn’s view, “it is normal science, in which Sir Karl’s sort of testing does not occur, rather than extraordinary science which most nearly distinguishes science from other enterprises”, and therefore a demarcation criterion must refer to the workings of normal science (Kuhn 1974, 802). Kuhn’s own demarcation criterion is the capability of puzzle-solving, which he sees as an essential characteristic of normal science.