As the philosopher of science Nancy Cartwright points out, laws are “descriptions of what regularly happens, not regular associations or singular causings that occur with regularity.” In other words, what Cartwright is saying is that epistemologically laws do not capture the complexities of the world they are intended to describe. In a sense, they are not as true or clear cut in the ordinary sense that the sky is blue is true. Laws, she argues, are uncovered only under certain conditions and thus only tell us that within a given capacity an object behaves in a certain way as a result of being in a particular circumstance. To illustrate this point, one of the examples she provides is that of gravity—Newton’s law of universal gravitation.
As Cartwright correctly points out, in the real world we do not just use Newton’s law. In fact, there are many other forces that must be accounted for such as inertia or electromagnetic forces. She argues, it is best to understand such “laws” as features of a model in which only takes account that particular force. That is to say, such laws are manifestations of models that assume such forces exist in isolation. The conclusion is inevitable. Taking such laws in isolation is not useful in the full extent of understanding the mechanics of the real world. For the sake of further clarification, this is not to say, as many have charged Cartwright with, that in general laws are not useful. Rather, given a specific context, laws are not useful in the sense that they actually tell us anything about the relationships between the constituents—instead, it is limited to particular conditions and therefore gives us insight into the constituents to the extent of their particular environment.