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 just stumbled into this discussion after reading an article about why mathematicians and scientists dislike traditional, Socratic philosophy, and my mindset is fresh off that article.
It was a fantastic read, but the underlying theme that I feel is relevant to this discussion is this:
Socratic philosophy treats logical axioms as "self-evident truths" (i.e. I think, therefore I am).
Mathematics treats logical axioms as "propositions", and uses logic to see where those propositions lead (i.e. if you have a line and a point, the number/amount of lines that you can draw through the point that's parallel to the original line determines what type of geometry you are working with (multidimensional, spherical, or flat-plane geometry)).
Scientists treat logical axioms as "hypotheses", and logical "conclusions" as testable statements that can determine whether those axioms are true or not (i.e. if this weird system known as "quantum mechanics" were true, then we would see an interference pattern when shooting electrons through a screen with 2 slits).
So I guess the point that we should be making is this: which philosophical approach towards logic should we take to study ethics? I believe Wei_Lai would say that the first approach, treating ethical axioms as "self-evident truths" is problematic due to the fact that a lot of hypothetical situations (like my example before) can create a lot of contradictions between various ethical axioms (i.e. choosing between telling a lie and letting terrorists blow up the planet).
Thank you for an awesome read. :)