You're perhaps using H₂O as a description rather than as a rigid designator, which sidesteps the point rather than addresses it.

So let's use Hesperus and Phosphorus instead. Hesperus is seen only in the evening; Phosphorus only in the morning. It took empirical observation and theorising for us to understand that they are the same - Venus.

But in every possible world, Hesperus = Phosphorus.

Which is to say, in supposing a possible world in which there was an object named Hesperus and another, different object names Phosphorus, we stop using these terms to talk about Venus. At least one of the objects is not the same as Venus. It's not that Hesperus is not the very same as Phosphorus in that world, but that there is something else that just happens to have the name Phosphorus or Hesperus.

This is a grammatical point that comes directly from the formalised language of possible world semantics. You can take it or leave it as you wish, but if you leave it you also leave the logical structure of possible world semantics and the ensuing capacity to keep modal sentences consistent.

If H2O was a mineral in a universe with different laws, wouldn't it be H2O*? — RogueAI

The point is that the expression confuses what would be going on. There is no possible world in which H₂O is not water. There may be a possible world in which the term "H₂O" is used to refer to something else.

There is no possible world in which H₂O is not water. — Banno

There is no possible world in which XYZ is not water. — TwinBanno

That doesn't say anything.

It seems strange to incorporate 2D semantics where the referent isn't subject to modalities like Hesperus or Phosphorus.

Hence the need for an actual observation to take place to endow it with the name 'Venus'.

Water and H2O are two different things... — RogueAI

Except where the words coextend.

Presumably, the different laws of nature that allow H2O to become a mineral would affect either the Hydrogen, Oxygen, or chemistry of their interaction, so that you're really talking about something other than what we mean by H2O. — RogueAI

This is Kripke in a nutshell. Kripke demands that we pay attention to use. The rigid designator is like a tracking device stuck on a particular usage.

This is Kripke in a nutshell. — frank

Sorry, that's a de re. De dicto, de jure, and de facto's take precedence to determine the de re's.

Okey dokey.

You're perhaps using H₂O as a description rather than as a rigid designator, — Banno

I don't think so. From Stanford:

A rigid designator designates the same object in all possible worlds in which that object exists and never designates anything else.

My claim is that H20 is not in all cases the same object as water. The molecular structure can differ. H20 always has the same structure. Water does not. Water contains minerals and contaminants. H20 does not. A chemical analysis will reveal this. If they are the same object then they could be used interchangeably in all possible situations. They cannot.

So let's use Hesperus and Phosphorus instead. — Banno

But that missed the point. Hesperus and Phosphorus designate the same object. In many cases H20 and water also designate the same object but not in all cases.

But that missed the point. — Fooloso4

On the contrary, it re-makes the point your pedantry tries to ignore.

You want to use "water" for impure H₂O. Go ahead. Pure water is necessarily the very same thing as H₂O. Point made.

You want to use "water" for impure H₂O. Go ahead. — Banno

Impure H₂O?

H₂O with lumps in.

You want to use "water" for impure H₂O. Go ahead. Pure water is necessarily the very same thing as H₂O. — Banno

It is not a matter of how I want to use the term water, it is the common usage for the stuff that comes out of the tap, the stuff in lakes and rivers and rain. It is not pure H20. Generally potable water is considered pure but it contains minerals and so is not H20, it is a mixture of H20 and other stuff.

Sure, understood; but pure water = H₂O in all possible worlds.

I do not know anything about all possible worlds and very little about the actual world we live in, but
I see no problem with this: a molecule of water = H20. Or molecular grade water = H20.

Good for you. I don't see the point in our repeating ourselves.

Pure water is necessarily the very same thing as H₂O. — Banno

Perhaps, but the question and topic of the OP are not about pure water. @Fooloso4 makes a valid point that H₂O is necessarily water "but water is not necessarily H₂O".

I understand rigid designators to refer to some particular physical object or stuff regardless of the name, so whether that physical stuff is "water" or "H₂O" depends on which stuff is designated.

I'm not seeing a point to this conversation.

https://thephilosophyforum.com/discussion/comment/243503

Luke I'm not seeing a point to this conversation. — Banno

The point is that it is a flaccid designator.

It seems as if there are three different issues under discussion here:

1) Whatever distinction the OP is making. 2) The distinction I am making. 3) Kripke's a posteriori necessities.

The point is that it is a flaccid designator. — Fooloso4

Not quite. Water is bouncy. Elastic.

See a drop of water fall into a pool of water in slow motion. It bounces back.

I actually don't know if the shots I have seen about this referred to pure water, dirty water, someone named Walter in a different universe, contaminated water in a third world country, or to H20 in any world, universe or country.

Water comes out of my faucet and H₂O is our model of a wee bit of that.
I guess the word "water" and H₂O shares reference.
Does that work?