 Steel (2008) has proposed a form of reasoning that he calls “comparative process tracing”. Steel’s proposed solution is that even in the absence of strong evidence as to what mechanism(s) operate in a target system compared to a model system, scientists can compare the two systems with respect to certain crucial nodes in the respective causal structures, namely those where the two systems are most likely to differ. This can break the regress by providing evidence that the two systems are similar enough to warrant extrapolations, yet it is not necessary to already have an understanding of the target systems that matches the knowledge about the model system.