 For externalists about the object of understanding, especially concerning phenomena “out there in the world”, the proposed objects vary. For instance, there is some support for the idea that the objects are nomic relations, or relationships according to which individual events and other phenomena are explained by laws, and upper-level laws are explained by lower-level or more fundamental laws (Railton 1978). Another view is that the objects are causal relations (Salmon 1984; Lipton 1991 [2004]), or more generally dependence relations (Kim 1974, 1994; Grimm 2014, 2017; Greco 2014; Dellsén 2020), where causation is usually taken to be just one species of dependence.