The second approach, which has proven fruitful for guiding a host of research and development efforts, relies on arguments that are pragmatic in nature. One such argument, which we put forth about a decade ago (Abd-El-Khalick et al. 1998 ) , goes something like this: Disagreement on specific conceptualizations of NOS should not be surprising given the multifaceted and complex nature of the scientific enterprise. Also, similar to scientific knowledge, conceptions of NOS are tentative and dynamic: they have changed (and continue to change) throughout the develop- ment of science and systematic thinking about its nature and workings (Abd-El- Khalick and Lederman 2000 ) .