Finds that many activities that have been called "problems" are merely exercises or tricks. Offers a clearer definition of the word "problem". Notes some of the classroom implications of the new insight. (Author/CCM)

This comment attempts to identify different "semiotic perspectives" proposed by the authors of this special issue according to the problems they discuss. These problems can be distinguished as problems concerning the representation of mathematical knowledge, the definition and objectivity of meaning, epistemological questions of learning and…