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I closed my previous post on method by noting I am getting increasingly skeptical of MacIntyre’s view that traditions are incommensurable with each other. Christian Hendriks made an excellent comment in response:

What would it look like for philosophical traditions to be more commensurable? It has seemed obvious to me for quite some time that many philosophical traditions are incommensurable; MacIntyre is attractive to me in large part because he addresses this problem (and addresses it as a problem rather than a neutral feature). I don’t mean “it seems obvious” to stand in for an argument here, but I can’t at this moment even imagine what it would look like for traditions to be more commensurable than MacIntyre claims. Can you elaborate on that? [emphasis in original]

It is a great question and one I will probably need to think through more fully. But I’d like to take a first stab at it here. MacIntyre’s usage of “incommensurable” comes largely from Thomas Kuhn; the term means that there is no common standard, literally common measure, between different traditions or paradigms of inquiry. So to reject incommensurability – to accept commensurability – is to say that there is some sort of common standard or measure between traditions. What then would that mean?

First, it’s worth noting the room that MacIntyre himself makes for commensurability: that incommensurable traditions can become commensurable. I mentioned the point briefly a few years ago, but didn’t explain how this could happen, in MacIntyre’s view. His claim is that a tradition can fail by its own standards, facing an epistemological “crisis”, in Kuhn’s terms. At that point it becomes possible for another “rival” tradition to account for that failing tradition, by its own standards, better than it accounts for itself (without the rival tradition itself failing). Those standards can effectively be taken in common.

That much is important, but it doesn’t answer the question Christian actually asked. So far I’ve just pointed out an aspect of MacIntyre’s position, but I’d claimed I’m getting skeptical of that position; Christian specifically asked what it would look like for traditions to be more commensurable than MacIntyre claims. What then would that be?

The first and most straightforward part of the answer is that a very large number of the differences between traditions do not go all the way down to the foundations or roots; there are mid-level points of agreement that can serve as common measures. I think this is one reason the idea of human rights has gotten as far as it has: it is not so hard for people of vastly different traditions to agree that governments should not arbitrarily kill or detain their citizens, even though their reasons for making that claim may differ. So there can in many cases be significant commensurability at a more derivative or practical level even in those cases where there is incommensurability at a more foundational and theoretical level. MacIntyre rarely discusses this sort of case, but I think they’re important.

But even at the level of theoretical foundations, I think resolving differences may be easier than MacIntyre portrays – for reasons that refer to the history and philosophy of science, as MacIntyre does. MacIntyre does sometimes point out, rightly, that traditions of inquiry are not unitary, and contain conflict within them; but I think he does not go far enough with the point. A while ago I offered an account of the history of biology that could be interpreted in MacIntyrean or Kuhnian terms, where it was basically a single paradigm of intelligent design replaced by a single paradigm of Darwinian evolution. But as I’ve been reading more in the history of biology, I have come to see it did not work that way: Lyell’s intelligent-design approach was a relatively new theory in Darwin’s day, one around the same time as other evolutionists (notably Lamarck) who competed with Darwin; and Darwin’s theory itself was not widely accepted until after it came into synthesis with the theories of Mendelian geneticists (who were initially opposed to it).

The point of this excursus into biology is to point out that whatever paradigms existed were very much in flux, so much so that they could barely even constitute traditions of inquiry. Their disagreements were difficult to resolve, but people found ways to do so, using whatever standards they had at their disposal – above all recognizing inconsistencies within the theoretical frameworks they had marshalled to date. The need to reconcile inconsistencies is one of the formal or weak standards of rationality that MacIntyre agrees are more or less universal, but are too thin to be consistently applied across traditions and paradigms.

In the natural sciences, the inconsistencies have primarily to do with empirical evidence, but it is crucial that it is not merely a matter of “the evidence” being incompatible with “the theory” – for what we take to be evidence is always informed by the theory. There are cases where “the evidence” tells us something that our theories tell us it shouldn’t, and those cases are vital to science – but they do not in themselves refute the theory,as the Duhem-Quine thesis reminds us. So Lakatos famously and rightly said, staking out a ground against both Popper and Kuhn: “It is not that we propose a theory and Nature may shout NO; rather, we propose a maze of theories, and nature may shout INCONSISTENT”.

But it is not merely nature that may shout INCONSISTENT. Once we acknowledge (rightly) that what’s proposed in any discipline is a “maze of theories”, then resolving the inconsistencies in that maze becomes a way for it to advance, and it is not necessarily empirical evidence that is responsible for that inconsistency. Sometimes that advancement may come from outsiders, whose own theories are able to provide a way of keeping important theories in the original maze while jettisoning those with inconsistencies. There is no cut-and-dried universal procedure by which one can regularly accomplish this; MacIntyre is right about that. Inconsistencies look different in every case. But Mendelian genetics and Darwinian evolution were able to become a synthesis, one that explained the world better than either could do alone, and it seems to me that the same is possible for philosophical traditions.