What do I mean by "morality isn't logical"? I mean in the same sense that mathematics is logical but literary criticism isn't: the "reasoning" we use to think about morality doesn't resemble logical reasoning. All systems of logic, that I'm aware of, have a concept of proof and a method of verifying with high degree of certainty whether an argument constitutes a proof. As long as the logic is consistent (and we have good reason to think that many of them are), once we verify a proof we can accept its conclusion without worrying that there may be another proof that makes the opposite conclusion. With morality though, we have no such method, and people all the time make moral arguments that can be reversed or called into question by other moral arguments. (Edit: For an example of this, see these posts.)
Without being a system of logic, moral philosophical reasoning likely (or at least plausibly) doesn't have any of the nice properties that a well-constructed system of logic would have, for example, consistency, validity, soundness, or even the more basic property that considering arguments in a different order, or in a different mood, won't cause a person to accept an entirely different set of conclusions. For all we know, somebody trying to reason about a moral concept like "fairness" may just be taking a random walk as they move from one conclusion to another based on moral arguments they encounter or think up.
In a recent post, Eliezer said "morality is logic", by which he seems to mean... well, I'm still not exactly sure what, but one interpretation is that a person's cognition about morality can be described as an algorithm, and that algorithm can be studied using logical reasoning. (Which of course is true, but in that sense both math and literary criticism as well as every other subject of human study would be logic.) In any case, I don't think Eliezer is explicitly claiming that an algorithm-for-thinking-about-morality constitutes an algorithm-for-doing-logic, but I worry that the characterization of "morality is logic" may cause some connotations of "logic" to be inappropriately sneaked into "morality". For example Eliezer seems to (at least at one point) assume that considering moral arguments in a different order won't cause a human to accept an entirely different set of conclusions, and maybe this is why. To fight this potential sneaking of connotations, I suggest that when you see the phrase "morality is logic", remind yourself that morality isn't logical.
I agree that it's going to take a lot of work to fully clarify our concepts. I might be able to assign a less remote probability to 'morality turns out to be impossible to carefully reason with' if you could give an example of a similarly complex human discourse that turned out in the past to be 'impossible to carefully reason with'.
High-quality theology is an example of the opposite; we turned out to be able to reason very carefully (though admittedly most theology is subpar) with slightly regimented versions of concepts in natural religion. At least, there are some cases where the regimentation was not completely perverse, though the crazier examples may be more salient in our memories. But the biggest problem with was metaphysical, not semantic; there just weren't any things in the neighborhood of our categories for us to refer to. If you have no metaphysical objections to Eliezer's treatment of morality beyond your semantic objections, then you don't think a regimented morality would be problematic for the reasons a regimented theology would be. So what's a better example of a regimentation that would fail because we just can't be careful about the topic in question? What symptoms and causes would be diagnostic of such cases?
By comparison, perhaps. But it depends a whole lot on what we mean by 'morality'. For instance, do we mean:?
Morality is the hypothetical decision procedure that, if followed, tends to maximize the amount of positively valenced experience in the universe relative to negatively valenced experience, to a greater extent than any other decision procedure.
Morality is the hypothetical decision procedure that, if followed, tends to maximize the occurrence of states of affairs that agents prefer relative to states they do not prefer (taking into account that agents generally prefer not to have their preferences radically altered).
Morality is any decision procedure that anyone wants people in general to follow.
Morality is the human tendency to construct and prescribe rules they want people in general to follow.
Morality is anything that English-language speakers call "morality" with a certain high frequency.
If "value is complex," that's a problem for prudential decision theories based on individual preferences, just as much as it is for agent-general moral decision theories. But I think we agree both there's a long way to go in regimenting decision theory, and that there's some initial plausibility and utility in trying to regiment a moralizing class of decision theories; whether we call this regimenting procedure 'logicizing' is just a terminological issue.
What I mean by "morality" is the part of normativity ("what you really ought, all things considered, to do") that has to do with values (as opposed to rationality).
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