On the standard picture there are three kinds of facts. Some facts cannot have been otherwise. These facts include the conceptual truths (e.g., the fact that Rebecca is taller than Abe if Abe is shorter than Rebecca) and the mathematical truths (e.g., that 2 + 1 = 3). The remaining facts (i.e., the "contingent" ones) are divided between the other two classes: (1) the laws of nature (and their contingent logical consequences), such as the fact that all copper objects are electrically conductive, and (2) the "accidents," such as the fact that Jones has ten fingers and the fact (one can suppose it is a fact, though humanity may never discover it) that there never exists a solid gold cube larger than a cubic mile.

It is widely believed that one of science's chief goals is to discover the laws of nature. Philosophers have studied the role that the concept...