There would be an observable difference in either world. — Hanover

In one possible world babies suffer if they're murdered and it's immoral to murder babies.

In another possible world babies suffer if they're murdered but it's not immoral to murder babies.

In both worlds we believe that it is immoral to murder babies.

What is the observable difference between each world?

In one possible world babies suffer if they're murdered and it's immoral to murder babies.

In another possible world babies suffer if they're murdered but it's not immoral to murder babies.

In both worlds we believe that it is immoral to murder babies.

What is the observable difference between each world — Michael

Absolutely none. So why don’t we dump moral realism and moral subjectivism and all other moldy conformist dictums stuck in the 18th century, which blithely ignore all the exciting ideas coming from current research in evolutionary biology, anthropology , psychology and language studies?

That you think "moral" = "rational"; and "immoral" = "irrational" ... — Vaskane

Another vapid strawman.

:shade: Go troll someone else, kid.

Plenty of rational "immoral" choices to make in life. Why not just say good and evil? It's the same pathetic equation. — Vaskane

I agree here. There are an infinity of competing rationalities out there. But we do tend to find some value systems more pragmatically useful than others, given our purposes within our local communities. Do you suppose there is anything like a progress of pragmatic rationality?

...injury... — frank

Debatable as to whether that counts as "injury" - to pick an example, scarring as a ritual in transitioning to adulthood. But yes, I agree. Part of the trouble here is that possible world semantics is extensional, so it perhaps is not able to pick up on such nuance.

Forgive what was said late on Christmas night. What I would take issue with is the ambiguity of @Michael mixing two modal contexts - possible and ought. What's unclear is how we work simultaneously with both modalities. So, by way of an example, if one ought do some thing, does it follow that one ought do that thing in every world in which it is possible? Note that here we are treating actions as individuals, which may itself be problematic, and the issue seems to be one of accessibility between possible worlds - the possible worlds that are accessible may be only the ones in which doing that things is possible.

All of which is to point out that Michael's treatment might be far less clear than he seems to suppose.


Edit: By way of an example,

In one possible world babies suffer if they're murdered and it's immoral to murder babies.

In another possible world babies suffer if they're murdered but it's not immoral to murder babies. — Michael

Perhaps the way to pars this is that, if the first world is accessible, then the second world isn't. At the very least, it remains to be shown that the second is accessible from the first. That is, if in some world it is immoral to murder babies, then maybe in no possible world accessible from that world is it moral to murder babies.

But my point here is that without the formal background it is not obvious how we can do what Michael wants to do here.

Or is there a way to introduce the modality of "ought" into a possible world semantics, other than using accessibility?

Or is there a way to introduce the modality of "ought" into a possible world semantics, other than using accessibility? — Banno

There's this SEP article about deontic logic. There's some mention of possible worlds, but I think moral commitments come first. If P is the proposition that it's immoral to kill babies, and you believe P, then you will say P is necessarily true. You'll say that anyone who believes there's a possible world at which P is false is deluded.

Notice that toward the end of that article they allude to the fact that normativity is a pit with no bottom. If you jump into that pit, you may never be seen again.

In both worlds we believe that it is immoral to murder babies. — Michael

Why are we unable to determine right and wrong in the non-naturalist world?

There's this SEP article about deontic logic. — frank

Yes, that gives some indication of the issues involved. I think @Michael skates over too much.

If water is H₂O, then necessarily water is H₂O. There is no prima facie contradiction in water being made of other stuff, but once it is found to be made of H₂O, the alternatives are pruned from the tree of possibilities.

Perhaps, If one ought not murder babies, then necessarily one ought not murder babies. There is no prima facie contradiction in murder babies, but once it is found that one ought not murder babies, the alternatives are pruned from the tree of possibilities.

@Michael has not shown this not to be the case.

but once it is found that one ought not murder babies, the alternatives are pruned from the tree of possibilities — Banno

I think so, yes. So if you've found that murdering babies is immoral, you might read about the history of infanticide in a purely moral light.

Yep - for the longest time infanticide was considered an acceptable expediency. Now, not so much. Pederasty has a similar history.

There's something specious in the question Michael asks about how worlds differ given moral truths. they differ specifically in the truth of those moral statements...

There's something specious in the question Michael asks about how worlds differ given moral truths. they differ specifically in the truth of those moral statements... — Banno

I don't quite follow.

I don't quite follow. — frank

Well, I'm not sure I do, either.

From the OP:

Let us imagine that the concept of categorical/unconditional imperatives/obligations was sensible. Let us also imagine that these are true. What then? How would this world differ from one without objective/inherent/intrinsic/absolute/universal morality (henceforth simply referred to as "morality")? — Michael

The difference would be exactly the truth of the obligation...

Michael seems to imply that there might be no other difference. First, the existence of the obligation is sufficient to differentiate the two words; second, the assumption is that obligations exist only within worlds and not between them; that obligations are not transworld. Hence the argument that an obligation may be necessarily true - true in all possible worlds.

All this is by way of pointing out that the structure of these relations is not as clear as might be supposed.

The difference would be exactly the truth of the obligation...

Michael seems to imply that there might be no other difference. First, the existence of the obligation is sufficient to differentiate the two words; — Banno

I think he's looking for a difference beyond those two things, though. Think of these two situations:

Situation 1: The Holocaust was inherently evil. It's evil in all possible worlds because there just can't be a Holocaust that doesn't have the property of evil.

Situation 2: The Holocaust is evil because we think of it that way, not the other way around. We could presently live in a world where the attitude behind the Holocaust (eugenics) prevailed, and everyone thinks of it as a great thing that made the world better. We just happen to live in the one where it's viewed as unbelievably horrible.

What practical difference is there between situation 1 and 2? How would your life be different? How would anybody's life be different?

Is the suggestion that these two worlds might be identical? But there is a difference - in one the holocaust is inherently evil (whatever that might mean) but in the other it is evil by...what, popular vote?

Again, the structure of these relations is not as clear as might be supposed.

Is the suggestion that these two worlds might be identical? — Banno

How does the Holocaust being inherently evil show up in something I can sense? What would I see that tells me I'm in the world of inherent evil? What would I hear or taste? Smell or feel?

How does the Holocaust being inherently evil show up in something I can sense? — frank

Well, talk of experience is different again. A third layer, so we have alethic, deontic and now epistemic modalities.

And so back to my point: the framework being used here is far from clear.

Ok, but how would you answer the question?

It's not an answerable question.

If water is H₂O, then necessarily water is H₂O. There is no prima facie contradiction in water being made of other stuff, but once it is found to be made of H₂O, the alternatives are pruned from the tree of possibilities. — Banno

That's because "H₂O" and "water" are rigid designators that refer to the same thing. If ethical non-naturalism is true then "immoral" and "harmful" are not rigid designators that refer to the same thing.

Can there be a posteriori necessity without rigid designators referring to the same thing?

A third layer, so we have alethic, deontic and now epistemic modalities.

And so back to my point: the framework being used here is far from clear. — Banno

Considering deontic logic, is OA → ◻OA an axiom?

If it is, is it an axiom by choice or by necessity?

There's something specious in the question Michael asks about how worlds differ given moral truths. they differ specifically in the truth of those moral statements... — Banno

I've been clearer in subsequent posts. I'm asking about observable differences.

I believe that eating dirt will make me sick. I eat dirt. If my belief is true then I will be made sick, if my belief is false then I won't be made sick. This is an observable difference.

I believe that it is immoral to eat meat. I eat meat. If my belief is true then... what? If my belief is false then... what? In either case I just eat meat. I can't think of an observable difference between the belief being true and the belief being false.

If there is no observable difference then what is our motivation to be moral?

Why are we unable to determine right and wrong in the non-naturalist world? — Hanover

I'm not saying that we're unable. But we're not infallible, and so it's possible that our moral beliefs are wrong. I am simply asking about the observable difference between our moral beliefs being true and those same moral beliefs being false. If ethical non-naturalism is true then it seems to me that there would be no observable difference.

But as a related question, if ethical non-naturalism is true then how can we determine right and wrong? Can there be empirical evidence of non-natural facts? Or if it's determined by reason alone then from which premises can we derive moral truths?

If ethical non-naturalism is true then "immoral" and "harm" are not rigid designators that refer to the same thing. — Michael

Neither is the kind of thing that could be a rigid designator. Harm, in the sense you're using it, is a transient state. Immoral is an adjective. Using possible world semantics is going to cause confusion. That's because different starting assumptions will give you different possibilities (and impossibilities).

Then "harmful" rather than "harm".

Then "harmful" rather than "harm". — Michael

That's an adjective. You can use the Holocaust as a rigid designator.

That's an adjective. — frank

As is "immoral" according to you.

As it "immoral". — Michael

Right. Adjectives can't be rigid designators.

Right. Adjectives can't be rigid designators. — frank

Then I repeat what I said before:

Does necessary a posteriori truth without rigid designators that refer to the same thing make sense? If not then if ethical non-naturalism is true then "it is immoral to harm others" is not a necessary a posteriori truth.

Does necessary a posteriori truth without rigid designators make sense? If not then if ethical non-naturalism is true then "it is immoral to harm others" is not a necessary a posteriori truth. — Michael

I could work out a scenario in which someone would conclude that it is (the bolded part), but the point is that possible world semantics always starts with a set of assumptions about how the world works, and it helps us analyze the way we navigate through and assess statements that arise from those assumptions. It's no good for weighing those starting assumptions. That's done by other means.

I could work out a scenario in which someone would conclude that it is (the bolded part) — frank

How? Until Kripke's Naming and Necessity almost all philosophers thought a posteriori necessity impossible. It was only with his explanation of rigid designators that a strong case for them was made. If you can make a case for a posteriori necessity without rigid designators then that would be quite the philosophical breakthrough.

Kripke’s examples are not the only ones that could be appealed to in order to shed doubt on the coextensiveness of necessity and a prioricity. Some other problematic cases are listed below (Chalmers 2002a; cp. Chalmers 2012, ch. 6).

Mathematical truths. It is common to hold that all mathematical truths are necessary. But on the face of it, there is no guarantee that all mathematical truths are knowable a priori (or knowable in any way at all). For example, either the continuum hypothesis or its negation is true, and whichever of these claims is true is also necessary. But for all we know, there is no way for us to know that that proposition is true.
Laws of nature. Some necessitarians about the natural laws (see section 2) believe that the laws hold in all metaphysically possible worlds. But they are not a priori truths.
Metaphysical principles. It is often believed that many metaphysical theses are necessary if true, e.g., theses about the nature of properties (e.g., about whether they are universals, sets or tropes) or ontological principles like the principle of unrestricted mereological composition (which says that for any things there is something that is their sum). But it is not obvious that all truths of this kind are a priori. (For discussion, see Chalmers 2012, §§6.4–6.5; Schaffer 2017.)
Principles linking the physical and the mental. Some philosophers hold that all truths about the mental are metaphysically necessitated by the physical truths, but deny that it is possible to derive the mental truths from the physical ones by a priori reasoning (see Hill & McLaughlin 1999; Yablo 1999; Loar 1999; and Chalmers 1999 for discussion). On that account, some of the conditionals that link physical and mental claims are metaphysically necessary but not a priori. — SEP

The formatting got screwed up there, but look at the bolded section that starts with "Laws of nature." This is the primary root of moral realism: that it comes from God. Some cultures maintained that we're born knowing the difference between good and evil (Persians), but in the Hebrew outlook, we aren't. We have to learn it by becoming acquainted with God's laws. That would be a form of a posteriori necessity.

This is the primary root of moral realism: that it comes from God. Some cultures maintained that we're born knowing the difference between good and evil (Persians), but in the Hebrew outlook, we aren't. We have to learn it by becoming acquainted with God's laws. That would be a form of a posteriori necessity. — frank

So let's grant that the existence of God entails that there are necessary moral truths. Why be moral? What if God commands that non-believers ought be stoned to death? Would you stone non-believers to death?

Assume, for the sake of argument, that God does not reward the moral or punish the immoral.

I, for one, am not motivated simply by the belief (or knowledge) of what I ought to do.

So let's grant that the existence of God entails that there are necessary moral truths. — Michael

? You were asking how there could be necessarily true statements known a posteriori. Did you understand the answer?

What is the motivation to be moral? — Michael

Love.