ABSTRACT
There are at least two kinds of laws of nature: laws of association and causal laws. Laws of association are the familiar laws with which philosophers usually deal. These laws tell how often two qualities or quantities are co-associated. They may be either deterministic—the association is universal—or probabilistic. The equations of physics are a good example: whenever the force on a classical particle of mass m is f the acceleration is f/m. Laws of association may be time indexed, as in the probabilistic laws of Mendelian genetics, but, apart from the asymmetries imposed by time indexing, these laws are causally neutral. They tell how often two qualities co-occur; but they provide no account of what makes things happen.
