 However, HRT also faces serious problems. Recall that it presupposes that causes and effects can be sorted into types which are connected by a regularity. But it is unclear how the sorting can be achieved. What makes an event “like” another? Which aspects of the objects or events are relevant for the sorting? Many contemporary philosophers explicate the relevant notion of resemblance or similarity in terms of laws of nature. If there is a law of the form \(\forall x (A(x) \rightarrow B(x))\), then events similar to a token event \(a\) are simply events of the same type—other instantiations of \(A\)—and events similar to \(b\) are also just token events of the same type. However, it is a non-trivial task to give a satisfying account of what a law of nature is—to say the least.