Full Idea
The problem is to distinguish between laws and accidental generalizations, for laws have explanatory force while accidental generalizations, even if they are true, do not.
Gist of Idea
We must distinguish true laws because they (unlike accidental generalizations) explain things
Source
Wesley Salmon (Four Decades of Scientific Explanation [1989], 1.1)
Book Reference
Salmon,Wesley C.: 'Four Decades of Scientific Explanation', ed/tr. Humphreys,Paul [Pittsburgh 2006], p.14
A Reaction
[He is discussing Hempel and Oppenheim 1948] This seems obviously right, but I can only make sense of the explanatory power if we have identified the mechanism which requires the generalisation to continue in future cases.