 There are two reasons to care about the rationale for the law’s use of causation in the liability doctrines of tort and criminal law. The less relevant one here is the legal reformer’s motive, which is to assess what the best test for causation is and to recommend that such a test ought to be legislated for future legal use. The second, and the more relevant motive here, is the lawyer’s motive, which is to understand what the requirement for causation presently is under existing law. As was previewed in  section 1,  what the law provides on a given topic like causation is in part constituted by the function such a requirement serves in a body of law, and such function thus constitutes the third ingredient we need to consult as we reconstruct the law’s concept of causation.