The status of laws of nature has been the locus of a lively debate in recent philosophy. Most participants have assumed laws play an important role in science and metaphysics while seeking their objective ground in the natural world, though some skeptics (Giere, van Fraassen, Cartwright) have questioned this assumption. So-called Humeans look to base laws on actual, particular facts such as those specified in David Lewis’s Humean mosaic. Their opponents (including Maudlin) argue that such a basis is neither necessary nor sufficient to support the independent existence of scientific laws. This essentially metaphysical debate has paid scant attention to the details of scientific practice. It has mostly focused on so-called fundamental laws, ...