The Book of Why: The New Science of Cause and Effect (Penguin Science)

by Judea Pearl

In principle, counterfactuals should find easy application in the courtroom. I say “in principle” because the legal profession is very conservative and takes a long time to accept new mathematical methods. But using counterfactuals as a mode of argument is actually very old and known in the legal profession as “but-for causation.” The Model Penal Code expresses the “but-for” test as follows: “Conduct is the cause of a result when: (a) it is an antecedent but for which the result in question would not have occurred.” If the defendant fired a gun and the bullet struck and killed the victim, the firing of the gun is a but-for, or necessary, cause of the death, since the victim would be alive if not for the firing. But-for causes can also be indirect. If Joe blocks a building’s fire exit with furniture, and Judy dies in a fire after she could not reach the exit, then Joe is legally responsible for her death even though he did not light the fire.