As I read it, the rule does not forbid epiphenomena. Epiphenomena are caused by ordinary things that we can observe, so they are connected to us by causal links, even though we can never discover these links, since epiphenomena do not themselves cause anything we can observe.
This seems like a coherent way the universe could be, but isn’t. The machine simulating the universe could constantly scan it for blue objects and populate a list of all blue objects—but without using that list for anything further. This would be an epiphenomal blue-ness tag.
As I read it, the rule does not forbid epiphenomena. Epiphenomena are caused by ordinary things that we can observe, so they are connected to us by causal links, even though we can never discover these links, since epiphenomena do not themselves cause anything we can observe.
This seems like a coherent way the universe could be, but isn’t. The machine simulating the universe could constantly scan it for blue objects and populate a list of all blue objects—but without using that list for anything further. This would be an epiphenomal blue-ness tag.