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.

Taboo both "morality" and "logical" and you may find that you and Eliezer have no disagreement.

LessWrongers routinely disagree on what is meant by "

morality". If you think "morality" is ambiguous, then stipulate a meaning ('morality₁ is...') and carry on. If you think people's disagreement about the content of "morality" makes it gibberish, then denying that there are moral truths, or that those truths are "logical," will equally be gibberish. Eliezer's general practice is to reason carefully but informally with something in the neighborhood of our colloquial meanings of terms, when it's clear that we could stipulate a precise definition that adequately approximates what most people mean. Words like 'dog' and 'country' and 'number' and 'curry' and 'fairness' are fuzzy (if not outright ambiguous) in natural language, but we can construct more rigorous definitions that aren't completely semantically alien.Surprisingly, we seem to be even less clear about what is meant by "

logic". A logic, simply put, is a set of explicit rules for generating lines in a proof. And "logic," as a human practice, is the use a... (read more)I'd split up Eliezer's view into several distinct claims:

A

semanticthesis: Logically regimented versions of fairness, harm, obligation, etc. are reasonable semantic candidates for moral terms. They may not be what everyone actually means by 'fair' and 'virtuous' and so on, but they're modest improvements in the same way that a rigorous genome-based definition of Canis lupus familiaris would be a reasonable improvement upon our casual, everyday concept of 'dog,' or that a clear set of thermodynamic thresholds would be a reasonable regimentation of our everyday concept 'hot.'A

metaphysicalthesis: These regimentations of moral terms do not commit us to implausible magical objects like Divine Commands or Irreducible 'Oughtness' Properties In Our Fundamental Physics. All they commit us to are the ordinary objects of physics, logic, and mathematics, e.g., sets, functions, and causal relationships; and sets, functions, and causality are not metaphysically objectionable.A

normativethesis: It is useful to adopt moralityspeak ourselves, provided we do so using a usefully regimented semantics. The reasons to refuse to talk in a moral idiom are, in part thanks to 1 and 2, not strong eBy "morality" you seem to mean something like 'the set of judgments about mass wellbeing ordinary untrained humans arrive at when prompted.' This is about like denying the possibility of arithmetic because people systematically make errors in mathematical reasoning. When the Pythagoreans reasoned about numbers, they were not being 'sufficiently careful;' they did not rigorously define what it took for something to be a

numberor to have asolution, or stipulate exactly what operations are possible; and they did not have a clear notion of the abstract/concrete distinction, or of which of these two domains 'number' should belong to. Quite plausibly, Pythagoreans would arrive at different solutions in some cases based on their state of mind or the problems' framing; and certainly Pythagoreans ran into disagreements they could not resolve and fell into warring camps as a result, e.g., over whether there are irrational numbers.But the unreasonableness of the

disputants, no matter how extreme, cannot infect thesubject matterand make that subject matterintrinsically impossible to carefully reason with. No matter how extreme we make the Pythagoreans' eccentricities, as long as... (read more)There's a pseudo-theorem in math that is sometimes given to 1st year graduate students (at least in my case, 35 years ago), which is that

All natural numbers are interesting.Natural numbers consist of {1, 2, 3, ...} -- actually a recent hot topic of conversation on LW ("natural numbers" is sometimes defined to include 0, but everything that follows will work either way).

The "proof" used the principle of

mathematical induction(one version of which is):If P(n) is true for n=1, and the assertion

"m is the smallest integer such that !P(m)"leads to a contradiction, then P(n) is true for all natural numbers.and also uses the fact (from the Peano construction of the natural numbers?) that every non-empty subset of natural numbers has a smallest element.

PROOF:

1 is interesting.

Suppose theorem is false. Then some number m is the smallest uninteresting number. But then wouldn't that be interesting?

Contradiction. QED.

The illustrates a pitfall of mixing (qualities that don't really belong in a mathematical statement) with (rigorous logic), and in general, if you take a quality that is not rigorously defined, and apply a sufficiently long train of logic to it, ... (read more)

Well. Not a

purelyrandom walk. A weighted one.Isn't this true of all beliefs? And isn't rationality just increasing the weight in the right direction?

The word "morality" needs to be made more specific for this discussion. One of the things you seem to be talking about is mental behavior that produces value judgments or their justifications. It's something human brains do, and we can in principle systematically study this human activity in detail, or abstractly describe humans as brain activity algorithms and study those algorithms. This characterization doesn't seem particularly interesting, as you might also describe mathematicians in this way, but this won't be anywhere close to an efficient... (read more)

People do all sorts of sloppy reasoning; everyday logic also arrives at both A and ~A ; any sort of fuzziness leads to that. To actually be moral, it is necessary that you can't arrive at both A and ~A at will - otherwise your morality provides no constraint.

The actual quote is:

Thank you -- I knew I ADBOCed with Eliezer's meta-ethics, but I had trouble putting down in words the reason.

You are not using the same definition of logic EY does. For him logic is everything that is not physics in his physics+logic (or territory+maps, in the previously popular terms) picture of the world. Mathematical logic is a tiny sliver of what he calls "logic". For comparison, in an instrumentalist description there are experiences+models, and EY's logic is roughly equivalent to "models" (maps, in the map-territory dualism), of which mathematics is but one.

Every act of lying is morally prohibited / This act would be a lie // This act is morally prohibited.

So here I have a bit of moral reasoning, the conclusion of which follows from the premises. The argument is valid, so if the premises are true, the conclusion can be considered proven. So given that I can give you valid proofs for moral conclusions, in what way is morality not logical?

... (read more)I like this post, and here is some evidence supporting your fear that some people may over-use the morality=logic metaphor, i.e., copy too many anticipations about how logical reasoning works over to their anticipations about how moral reasoning works... The comment is already downvoted to -2, suggesting the community realizes this (

please don't downvote it further so as to over-punish the author), but the fact that someone made it is evidence that your point here is valuable one.http://lesswrong.com/lw/g0e/narrative_selfimage_and_selfcommunication/83ag

The

practiceof moral philosophy doesn't much resemble the practice of mathematics. Mainly because in moral philosophy we don't know exactly what we're talking about when we talk about morality. In mathematics, particularly since the 20th century, we can eventually precisely specify what we mean by a mathematical object, in terms of sets."Morality is logic" means that when we talk about morality we are talking about a mathematical object. The fact that the only place in our mind the reference to this object is stored is our intuition is what make... (read more)

I think the term you are looking for is "formal" or "an algebra", not "logic".

You're mischaracterizing the quote that your post replies to. EY claims that he is attempting to comprehend morality as a logical, not a physical thing, and he's trying to convince readers to do the same. You're evidently thinking of morality as a physical thing, something essentially derived from the observation of brains. You're restating the position his post responds to, without strengthening it.