 Suggested Readings. The most authoritative and comprehensive statement of the DN and IS models is probably Hempel (1965b). This is reprinted in Hempel 1965a, along with a number of other papers that touch on various aspects of the problem of scientific explanation. In addition to the references cited in this section, Salmon (1989: 46ff.) describes a number of well-known counterexamples to the DN/IS models and discusses their significance.