 In a more general sense, the Nagel model has been criticized as exemplifying all the shortcomings of the orthodox view on science. For example, it conceives of theories as syntactic entities, and it views reduction as explanation cashed out in terms of the DN model (Hempel &amp; Oppenheim 1948), which has itself been challenged on many grounds, especially those regarding the asymmetry of explanation (for an overview that focuses on problems arising from reduction as explanation, see Craver (2007: chap. 2), and for problems concerning the DN model, see Salmon 1989).