Tom, think about the discovery of the relevance of RH as an addition to the file folder containing our knowledge of blood compatibility. In order to grasp it, we first need knowledge of blood type compatibility. Only because we know that A bloods are compatible can we discover an additional causal factor. If no other relevant causal factors existed, then simply knowing that “A bloods are compatible” would be sufficient for our purposes of blood transfusions (and the like). But our knowledge that A bloods are compatible is not an “out-of-context absolute.” We never (properly) hit upon knowledge and then decide, “I now know everything causally relevant here.” Rather, we must acknowledge that we know what we know, but that other things may be causally relevant. Discovering those things adds detail to our knowledge, but it does not contradict it.
I’ve heard (but haven’t independently researched) that the Alexander Wiener, who discovered RH factor, was one of the scientists who also discovered blood type. Apparently, he wasn’t stopped in his tracks by the new discovery. It further clarified the causal knowledge he’d already attained.
