There has been a good amount of discussion recently between those who prefer the potential outcomes approach and those who prefer the causal diagram/do-calculus approach. Since a letter I wrote has been used as an example in this discussion, I thought I'd add my two cents. 1/n First, it is worth noting that these two approaches are both ingenious ways to add methods for causal inference into our toolbox. They also happen to be very similar, and (usually) lead to the same results. 2/n