Proponents like David Hume and A.J. Ayer argue that laws are simply descriptive summations of what occurs in nature. They are contingent (meaning they could be otherwise) and are discovered a posteriori (after experience). For Hume, we don't actually experience "cause and effect" or objective necessity out in the world; we just experience a "constant conjunction" of events (i.e., event A is always followed by event B).

The Problem: How do we separate a true law from a silly accident? For example, if every single dog ever born at sea happened to be a cocker spaniel, that wouldn't mean we should use that generalization to make predictions. Ayer solved this with an Epistemic Regularity Theory, arguing that a law is a universal truth plus our willingness to use it to make predictions and deductively organize scientific statements.

Fred Dretske wasn't buying the Regularity approach. He argued that if laws rely on our human attitudes and willingness to make predictions, then unknown laws couldn't exist (which confuses what a law is with how we know it). Instead, Dretske proposed that laws tell us how things must occur.

In his Universals Theory, laws aren't just universal generalizations about particular objects; they are necessary relations between properties (universals). It's not just that "all Fs happen to be Gs". Rather, the very property of F-ness necessitates or "brings with it" G-ness.

Nancy Cartwright throws a wrench into the whole machine. She argues that the fundamental laws of physics don't actually state the facts. 

• There is a trade-off: laws can either be factually descriptive or provide explanations of particular cases, but they can't do both.

Why? Because in order to be completely exceptionless, laws have to assume highly idealized circumstances (like operating in a perfect vacuum). 

• Think of dropping a bowling ball and a feather from a tower. Newton's law of universal gravitation works perfectly to predict the bowling ball, but in reality, wind resistance interferes with the feather. 

Because the real world is messy and complicated, Cartwright argues that if we treat the law as absolutely true, we would have to count our observation of the feather as competing evidence. 

Instead, laws must be treated as strictly false, ceteris paribus (all other things being equal) statements. Instead of perfectly describing reality, they give us a model or "simulations" to help us determine possible causes in concrete situations.