File this one under “unglamorous yet underrated philosophical paragraphs”:
There are really two problems that fall under the label of ‘the problem of intertheoretic choice-worthiness comparisons’. The first problem is: “When, if ever, are intertheoretic choice-worthiness comparisons possible, and in virtue of what are intertheoretic comparisons true?”…The second problem is: “Given that choice-worthiness sometimes is incomparable across first-order normative theories, what is it appropriate to do in conditions of normative uncertainty?”
Here is an oversimplified way of putting his point. Let’s say you think utilitarianism is true with some probability, and Kantian deontology is also true with some probability. Can you aggregate the recommendations of these two theories “across the probabilities”? Not easily. The Kantian theory offers an absolute recommendation, but should that carry the day if deontology is true with only 7%? More generally, even less absolute theories do not offer comparable frameworks for cross-theoretical aggregation. How does 6% truth for maximin, 13% truth for prioritarianism, and 27% truth for cosmopolitan utilitarianism all add up? It’s not like calculating true shooting percentage in the NBA, because there is no common and commensurable understanding of “points” across the different frameworks. This aggregation problem is actually tougher than Arrow’s, at least once we recognize there is justifiably uncertainty about the true moral theory.
There is actually some related blog commentary on this issue. Overall MacAskill is on to one of the most important developments in consequentialist ethics over the last few decades.