How were the fake Galleons used to communicate without Harry's?

Question

The workings of the fake Galleon communication system is described very specifically in Order of the Phoenix:

Hermione soon devised a very clever method of communicating the time and date of the next meeting to all the members in case they needed to change it at short notice, because it would look so suspicious if people from different Houses were seen crossing the Great Hall to talk to each other too often. She gave each of the members of the D.A. a fake Galleon (Ron became very excited when he saw the basket at first, convinced that she was actually giving out gold).

"You see the numerals around the edge of the coins?" Hermione said, holding one up for examination at the end of their fourth meeting. The coin gleamed fat and yellow in the light from the torches. “On real Galleons that’s just a serial number referring to the goblin who cast the coin. On these fake coins, though, the numbers will change to reflect the time and date of the next meeting. The coins will grow hot when the date changes, so if you're carrying them in a pocket you’ll be able to feel them. We take one each, and when Harry sets the date of the next meeting he'll change the numbers on his coin, and because I’ve put a Protean Charm on them, they’ll all change to mimic his."

This appears to be a very simple system. Each individual coin is charmed to duplicate Harry's coin. So whatever appears on Harry's coin will appear on everyone else's coin as well.

Yet later in the series we see messages being passed from one coin to another without the use of Harry's coin. At the end of Half-Blood Prince Harry tells Ron and Hermione to rouse the DA members via the coins, yet he does not give them his coin nor does he tell them where his coin is so that they could use it:

Use anyone else who you can rustle up from the D.A., Hermione, those contact Galleons will still work, right?

If Hermione changed the numbers on her own coin, it should not have transmitted any message to anyone else's coin because their coins were duplicates of Harry's coin, not hers.

Similarly, in Deathly Hallows we find Neville and Luna both using their coins to send messages:

"Neville, she's all right, we've seen her —"

"Yeah, I know, she managed to get a message to me."

From his pocket he pulled out a golden coin, and Harry recognized it as one of the fake Galleons that Dumbledore's Army had used to send one another messages.

"These have been great," said Neville, beaming at Hermione. "The Carrows never rumbled how we were communicating it drove them mad.

Note that the above quote apparently claims that the D.A. had used the coins to send one another messages, something that was never mentioned in Order of the Phoenix and is certainly beyond the scope of the system Hermione described.

Also in Deathly Hallows:

"I got the message," she said, holding up her own fake Galleon, and she walked over to sit beside Michael Corner.

And:

"We're fighting, aren't we?" said Dean, taking out his fake Galleon. "The message said Harry was back, and we were going to fight! I'll have to get a wand, though —"

Once again, these are communications that were made without the use of Harry's coin.

So when and how exactly did the communication system change? How did it go from a bunch of coins being charmed to duplicate whatever message was written on Harry's coin, to the ability for anyone to communicate with anyone?

Answer 1

Hermione never said Harry's coin was special in any way

Let's look at the quote you've provided:

"On these fake coins, though, the numbers will change to reflect the time and date of the next meeting... We take one each, and when Harry sets the date of the next meeting he'll change the numbers on his coin, and because I’ve put a Protean Charm on them, they’ll all change to mimic his."

The parts I emphasized are those to make us think Harry coin was "the main coin". But it may not be the case. Hermione does not explain all the details of the Protean Charm here, she only explains how DA members will use the coins in their situation. Meaning: Harry changes the date - everyone else receives the message. There may be more to the Protean Charm, but why mention it if changing info on Harry's coin is all they need for now?

Mind that Hermione also says:

"On real Galleons that’s just a serial number referring to the goblin who cast the coin. On these fake coins, though, the numbers will change to reflect the time and date of the next meeting."

She doesn't say: "Harry will send you whatever messages he wants". That also looks like restriction to the coins' functionality. But later we see that the coins are proper sms-like way of communication.

Looks to me like Hermione in the given quote wasn't explaining how the coins worked in general. She rather gave people instructions how they will use the coins in DA. That is, Harry was the only one to be allowed to change his coin, and the changing was limited (by the agreed rules, not magic) to date for safety reasons.

Answer 2

It was actually Hermione, who enchanted the coins

So that perfectly explains how was she able to spread the message without Harry's original coin - I don't see a reason Hermione wouldn't be able to charm another coin.

As to coins used to communication

"We're fighting, aren't we?" said Dean, taking out his fake Galleon. "The message said Harry was back, and we were going to fight! I'll have to get a wand, though —"

As have been said by Dumbledore, news spread very quickly around the Hogwarts, so I assume people heard that Harry's back, then they discovered that coins are active and were able to do the simple math.

Answer 3

It is possible that the Protean charm always works this way.

I can't find any canon information on this either way. Hermione never said anything about what would or wouldn't happen if one of the other students transfigured their own coin. Nor would that be surprising, since it wasn't relevant to the purpose of the coins, and the other students would presumably know how a Protean charm works anyway, even if they didn't know how to cast it yet.

It seems to me to be more elegant for the spell to always make all the enchanted items reflect one another (many-to-many) rather than having a master item that the others reflect (one-to-many) but that's hardly conclusive. It is also thought that the Dark Mark uses the Protean charm, in which case the charm is probably many-to-many rather than one-to-many, but the canon evidence on this point isn't conclusive either.

... but even if it doesn't, Dumbledore's Army could have modified the coins.

"...Protean Charm?... But that's... that's N.E.W.T. standard, that is."

It was surprising when Hermione was able to cast the Protean charm in her fifth year, but by the time of Deathly Hallows most of the students known to be in Dumbledore's Army were studying at N.E.W.T. level, and several were in their final year. If it was indeed necessary for them to re-enchant the coins to explicitly make them many-to-many, or to change which coin was the master, that would not have been an insurmountable obstacle.

Answer 4

This, perhaps, is not Canon in particular, but there is a logical reason for this if you look to folklore.

Thaumaturgy in many books is the ability to change many things, or one big thing, by using something that was a part of the original thing. Examples of this range from the Voodoo Witch making a doll, attaching one of your hairs and doing horrible things to you, to a variety of uses in the Dresdenverse (exploding hearts out of chests and benign tracking spells) It is all down to As above, So Below. Take a whole. Then take a small part of the whole. Cast the spell and whatever you do to the small part happens to the large part. I have read about this in so many books and folk tales both new and many that were around long before J.K. ever put pen to paper. I believe (without references, but it's likely) to be the inspiration for the Protean charm in the first place. Protean Charm is just J.K.'s name for the concept.

So here is the logical stretch that makes the whole thing make sense to me. All of the coins were a part of a single charmed group. Therefore each coin could logically be used in the same way as Harry's coin. Hermione never said that it was only Harry's coin that could be altered in order to communicate. Again, all of the fake coins were part of one group when charmed. Therefore, altering one should be reflected in all, thus giving the Potterverse the first mass text.

Again, this is a logical explanation based on folklore and endless sources in fantasy fiction. This is not canonical in any way. In truth I doubt J.K. gave it anywhere near this much thought. She had a conceptual idea, and she used it to excellent narrative effect. And to boot, can you imagine trying to fact check yourself through several books for very tiny details like this. I imagine it would be a nightmare. They actually employ fact checkers on certain TV series and sometimes Movie Series (Can you imagine Fact Checking the Friday the 13th movies for consistency?) I don't know that J.K. employed one or if it's a common thing with authors. Even so, this is a small enough detail to miss.