[deredede]

> Yes a client may be out of date and therefore show something different, but once it becomes up to date it should be showing the same state even if that means amending history. Why? Because the humans reading it will be confused otherwise! An app getting more data is something we intuitively understand, but if my client shows something and yours shows something else, we will conclude different meanings from it.

That's interesting because I have the complete opposite take and would hard disagree with this. I intuitively understand that if we both write messages at the same time, we will see them in different order. Snail mail has worked this way for centuries, and I very much prefer this to an app silently altering the content as time goes. It is confusing when it happens under my eyes (something moved at the top of the screen while I was reading the bottom, what was it?) and easily leads to missed messages especially in group conversations (my buddy sent a message with a poor connection at 11am, it is retried and sent at 2pm and appears before the lengthy discussion others had at noon).

[moring]

Snail mail has never claimed that a history of all messages, with that history having a current state, exists. If you send a paper letter, you don't have it yourself anymore. You might keep a copy, but that's a _copy_, not the letter you sent.

Messenger apps claim that such a history exists by showing you, well, that history. In the same way, messengers claim that a message order exists, by showing you the messages in that order. If something exists, then it is independent of the viewer. So the assumption that the message order is the same for all viewers is founded in how two people look at physical objects.

[deredede]

Messenger apps don't claim that this history should be global and consistent. The order in which messages were sent and received by my device is a perfectly fine (and I'd say intuitive) history. It is the order people (and their records, if they have some) would have had in mind in the old time.

I take a different conclusion from the way people look at physical objects: since your device (or even my other device) is a different physical object than my device, I'd be wholly unsurprised to find a different order there.

[lmm]

> Messenger apps don't claim that this history should be global and consistent.

The fact that we're talking about multiple people looking at the same chat - the fact that we do conceptualise it as "the same chat" and "the history" - implies that we think of it as a single thing. And I think messenger apps generally nudge us that way - e.g. setting the name of the chat usually sets it for everyone.

> It is the order people (and their records, if they have some) would have had in mind in the old time.

I don't think it is. If I pull my correspondence with person X out of my drawer or file, the only dates I have to order them by are the dates written on the letters - which are the letters they and I (if I keep carbons of the ones I send) wrote them on, not the dates I received them. If they sent me a postcard while on holiday and then a letter after returning that arrived sooner, I'll read them in one order on receipt and in a different order when looking back. Likewise if I have a memo of a phone call with them, that may be from before I received a letter that is nevertheless dated earlier.

[deredede]

> I think messenger apps generally nudge us that way - e.g. setting the name of the chat usually sets it for everyone.

That's a good point - maybe it's actually email that warped my mind.

> I'll read them in one order on receipt and in a different order when looking back

Also a good point, I was thinking more about business communication where the date the letter is received matters. Thinking back on it, I think the main difference is that the messenger apps might happily reorder message before (or while) I read them. And if only one order is to be available, the one of the most use to me for an instant messaging app is the one I received the messages in, but I get how for other use cases it would be different.

[kelnos]

Well, this really depends on the protocol and architecture of the system.

If it's a system where the server is merely store-and-forward, where it forgets its knowledge of messages after the recipients have received them, then sure, your stance is reasonable. The client will decide on message ordering; it can either just display in the order received from the server, or use any timestamps stored in the messages to order them (including possibly reordering if messages arrive out of order). The client has no other source of truth it can draw from, and so different clients may order things differently. (Even in this case, though, for many systems like this I would expect the server to timestamp the messages, and for all clients to honor those timestamps, so in practice everyone should see the same ordering.)

But Matrix is not such a system: each homeserver is the system of record for what messages have been received, and what order they go in. In this case, I would expect all users to see the same ordering, assuming all clients are able to query and receive the full history from the server.

[kevincox]

> I intuitively understand that if we both write messages at the same time, we will see them in different order.

I think you are thinking like a distributed systems designer. I would assume that if you asked 10 "random Americans" 9 of them would assume that someone managed to send their message first and would be surprised if their phone and their friends phone showed them messages in different orders.

[dwattttt]

Many people have had the experience of "I tried to call you, but you were calling me!"; I don't imagine they'd be surprised if "something weird" happened when you both tried to send a message at the "same" time.

[Kwpolska]

I would assume 9 of them would not care either way.

[kelnos]

I don't think you're arguing the same point. I agree with you that when two people write a message at nearly the same time, they may (initially) see those messages in a different order. But the server should decide what the ordering is, and inform the clients, which should update their view of the world.

The ordering the server decides may not be "correct" (for whatever definition of correct matters to you), but what is most important in this situation is consistency.

[zarzavat]

You need to know what ordering the other user is seeing, otherwise dangerous misunderstandings could result, for example you reply "yes" but it's in reply to a different message than the other side is seeing.

If I see that another message has arrived and my message could be misunderstood, I can correct that by sending another message. But if I don't know what ordering the other side is seeing then I don't know if my message is ambiguous or not.

The only way achieve that is to show a consistent ordering to both participants (or to force every message to be in reply to another message but that's too nerdy)