Why didn't Voldemort perform Priori Incantatem on Dumbledore's wand to see if he had discovered or destroyed any of his Horcruxes, after Gringotts?

Question

What if, what if, the boy knew about the others? Could he know, had he already acted, had he traced more of them? Was Dumbledore at the root of this? Dumbledore, who had always suspected him; Dumbledore, dead on his orders; Dumbledore, whose wand was his now, yet who reached out from the ignominy of death through the boy, the boy -

Harry Potter and the Deathly Hallows, Chapter 27, The Final Hiding Place

He then goes through each of his Horcruxes in his mind to deduce which ones Dumbledore might have suspected or discovered.

Which should he visit first, which was in most danger? An old unease flickered inside him. Dumbledore had known his middle name...Dumbledore might have made the connection with the Gaunts...Their abandoned home was, perhaps, the least secure of his hiding places, it was there that he would go first...

The lake, surely impossible... though was there a slight possibility that Dumbledore might have known some of his past misdeeds, through the orphanage.

Harry Potter and the Deathly Hallows, Chapter 27, The Final Hiding Place

By this time Voldemort has broken into Dumbledore's tomb and acquired his Elder wand. Surely his immediate reflex would be to perform Priori Incantatem to do a quick check, instead of wasting time assessing the weakest and most vulnerable locations. Also, it would be more reliable information than guesswork. He would have found out instantly that Dumbledore tried to get to the ring and the locket, by penetrating the defenses of the Gaunt shack and the cave, and would have known where to go check first.

Also, even without the Gringotts break-in, he must have definitely performed the spell out of curiosity, given that,

1. Dumbledore was his greatest enemy and was the leader of the anti-Voldemort movement. So performing Priori Incantatem on his wand would reveal a great many of his secrets to Voldemort.

2. The Elder wand being the most sought-after and the most powerful wand, and that Voldemort spent almost a year trying to find it, there must be a certain curiosity about the wand's past deeds, even if it weren't Dumbledore's.

3. Performing Priori Incantatem on a known enemy's wand seems like a natural thing to do, as seen from the following quote:

   "But he'll know soon, if he doesn't already, that mine's broken beyond repair," said Harry quietly.

   "No!" said Hermione, sounding frightened. "He can't know that, Harry, how could he -?"

   "Priori Incantatem," said Harry. "We left your wand and the blackthorn wand at the Malfoys', Hermione. If they examine them properly, make them re-create the spells they've cast lately, they'd see that yours broke mine, they'll see that you tried and failed to mend it, and they'll realize that I've been using the blackthorn one ever since."

   Harry Potter and the Deathly Hallows, Chapter 24, The Wandmaker

And we know he didn't because, if he had, he would have found out about the Horcrux hunt.

So, considering all these factors, why didn't Voldemort use Priori Incantatem on the Elder wand?

Answer 1

We don't know that the Dark Lord didn't use Priori Incantatem on the Elder Wand.

It would be a very logical course of action for the Dark Lord to use Priori Incantatem on the Elder Wand sometime after acquiring it. There is no explicit evidence that he did do this in the books, but his every small move isn't shown, so it's possible that he did and it wasn't mentioned because it wasn't significant enough to be mentioned. If he examined the Elder Wand and found nothing of use, this mightn't be important enough to mention.

He could've not known his Horcruxes were in danger because the spells used didn't show it.

Dumbledore didn't destroy the ring with a spell. He had destroyed the Horcrux in the ring using the Sword of Gryffindor, which wouldn't involve using a wand. He did retrieve the ring from the ruins of the Gaunts' house, but if he did that with spells that weren't uniquely identifiable as breaking through the Dark Lord's protection of his Horcrux, then seeing these spells in Priori Incantatem might not have raised the Dark Lord's suspicion.

Similarly, the spells Dumbledore used in the cave might not have been spells that would make the Dark Lord reasonably able to conclude that he had found the cave. For example, if the Dark Lord saw Dumbledore had previously cast the fiery rope, which never actually killed the Inferi, this could be a spell used in a duel or other similar case. As long as there were other situations that the spells Dumbledore used could be used in, the Dark Lord might not think this means his Horcruxes are in danger. He was confident he was the only one who knew about their existence.

It's also likely Dumbledore would've taken steps to prevent leaving clues for the Dark Lord.

Priori Incantatem is a common enough spell, it's not Dark magic or even particularly specialized knowledge. Dumbledore knew of its existence so we also he wasn't somehow unaware of it. In addition, he had known before he died that the Dark Lord would likely be able to obtain the Elder Wand after his death, which was part of why he planned to die willingly so he wouldn't be "defeated" and the true mastery of the Elder Wand would die with him since he and Severus Snape planned his death.

Since Dumbledore certainly planned ahead, and he knew about Priori Incantatem, it's likely that if he knew the spells he cast would give away that he knew about the Horcruxes, he would have done something to prevent the Dark Lord being able to find these clues. It's highly unlikely that Dumbledore would have overlooked the possibility of the Dark Lord using a relatively common spell and possibly discovering that Dumbledore knew about his Horcruxes. What Dumbledore does to conceal this, should the use of the spells be distinctive enough to make the Dark Lord suspicious, could be anything from "Obliviating" the wand somehow to sitting in his office casting random spells until the spells used to get into the Horcrux cave are hidden among the noise.

There may be a spell that removes previously cast spells from a wand’s memory. Mr. Diggory casts Deletrius on Harry’s wand to remove the Dark Mark shadow. It’s unclear whether this deletes it permanently from the wand’s memory or just stops the effect, but it’s a possibility l

“‘Prior Incantato!’ roared Mr Diggory.

Harry heard Hermione gasp, horrified, as a gigantic serpent-tongued skull erupted from the point where the two wands met, but it was a mere shadow of the green skull high above them, it looked as though it was made of thick grey smoke: the ghost of a spell.

‘Deletrius!’ Mr Diggory shouted, and the smoky skull vanished in a wisp of smoke.”
_{^{- Harry Potter and the Goblet of Fire, Chapter 9 (The Dark Mark)}}

We know from what "Moody" says, and the others don't contradict, when Harry's name is placed in the Goblet of Fire that magical objects can be Confunded.

“Because they hoodwinked a very powerful magical object!’ said Moody. ‘It would have needed an exceptionally strong Confundus Charm to bamboozle that Goblet into forgetting that only three schools compete in the Tournament … I’m guessing they submitted Potter’s name under a fourth school, to make sure he was the only one in his category …” _{^{- Harry Potter and the Goblet of Fire, Chapter 17 (The Four Champions)}}

Therefore, it is possible to use magic on a magical object to hide or conceal the truth. As Dumbledore is a highly skilled wizard, he would have almost certainly known how to and be able to successfully do this.

Also Priori Incantatem may have limits - it might not show every spell ever cast by the wand.

We know Priori Incantatem can show multiple spells that a wand has previously cast, but we don't know exactly how far back in a wand's history it can show. It might have a limited number of spells it could show, and in that case, by the time the Dark Lord gets the Elder Wand, the spells used in the Horcrux cave might have passed the limit, either because Dumbledore simply needed to cast that many spells by then or because he was purposefully trying to hide having used the spells in the Horcrux cave and the Gaunts' house.

Answer 2

Even if, contrary to @DavidS's answer, Priori Incantatem really reveals all the past spells, it's tedious work. Voldemort can assign someone to spend days going through hundreds of spells performed by Hermione's wand. But he only suspects the vulnerability of the Horcruxes mere hours before the Battle of Hogwarts commences. By then, he simply does not have time.

But he did have time to inspect the Elder Wand, because he retrieved it from Dumbledore's tomb weeks prior to the Battle of Hogwarts. We don't know if he may or may not have thought of using priori incantatem on the Elder Wand. But I got a feeling that he did not.

Firstly, even though he can assign someone to examine a normal wand like Hermione's, he would never trust anyone else to possess his precious Deathstick, even for a short inspection.

Secondly, in his mind he had the great Dumbledore killed, and possessed his wand against his will. And he will destroy the petty obstacles Dumbledore set for him with the Unbeatable Wand. What Dumbledore did (or did not) do does not matter now... He was invincible.

Answer 3

Edit - it's been pointed out that Harry seems to think they can go several layers deep when checking our Hermione's wand. Given that this seems to contradict Goblet Of Fire, I can see three possibilities.

1. Harry was wrong in his assumption that they'd get multiple spells from the wand (he was 14 and traumatised when Dumbledore explained it to him, after all).
2. Priori Incantato only works for spells cast within a time limit, rather than just "the last spell performed" and Priori Incantatum can ignore this time limit.
3. Genuine plot mistake. Meh, boring, let's ignore.

(Original answer follows)

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Because Priori Incantatem usually only shows the last spell a wand performed.

There are two uses of this type of spell in GOF. First, Amos Diggory uses the normal version to check the wand Winky is holding - this is Prior Incantato.

"Well, we'll soon see," growled Mr. Diggory, looking unimpressed. "There's a simple way of discovering the last spell a wand performed, elf, did you know that?"

Winky trembled and shook her head frantically, her ears flapping, as Mr. Diggory raised his own wand again and placed it tip to tip with Harry's.

"Prior Incantato!" roared Mr. Diggory.

Harry heard Hermione gasp, horrified, as a gigantic serpent­tongued skull erupted from the point where the two wands met, but it was a mere shadow of the green skull high above them; it looked as though it were made of thick gray smoke: the ghost of a spell.

"Deletrius!" Mr. Diggory shouted, and the smoky skull vanished in a wisp of smoke.

However, when Harry and Voldemort duel in the graveyard they inadvertently activate a far more powerful and rare form of this magic - Priori Incantatem.

Harry looked up at Dumbledore again, on whose face there was an arrested look.

"Priori Incantatem," he muttered.

His eyes gazed into Harry's and it was almost as though an invisible beam of understanding shot between them.

"The Reverse Spell effect?" said Sirius sharply.

"Exactly," said Dumbledore. "Harry's wand and Voldemorts wand share cores.

(dialogue skipped for brevity)

"So what happens when a wand meets its brother?" said Sirius.

"They will not work properly against each other," said Dumbledore. "If, however, the owners of the wands force the wands to do battle... a very rare effect will take place. One of the wands will force the other to regurgitate spells it has performed ­ in reverse. The most recent first. . . and then those which preceded it...."

The Elder wand has no known brother wands, and even if it did, Priori Incantatum is the result of a duel, so Voldemort would have no way of triggering it (otherwise it likely would have happened during the Ministry fight).

At best Voldemort could use Priori Incantato to check Dumbledore's last spell (Petrificus Totalus), which doesn't help him at all in working out which of his Horcruxes have been found.

Answer 4

Prior Incantato's spells can be removed

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First, it's not Priori Incatatem. It's Prior Incantato or just the "Reverse Spell", as the former one is the manifestation of two twin wands dueling each other.

The "Reverse Spell", however, is just a "history log" of the spells, jinxes and curses that the wand has performed in the past. As so, these "history records" can be deleted as shown in Harry Potter and the Goblet of Fire.

If you remember, Barty Crouch Jr, using Harry's stolen wand had performed Morsmondre spell. Later, when Amos Diggory performs Prior Incantato to see the previous spells, he removes the record of the spell using Deletrius:

"Prior Incantato!" roared Mr. Diggory.

Harry heard Hermione gasp, horrified, as a gigantic serpent-tongued skull erupted from the point where the two wands met, but it was a mere shadow of the green skull high above them; it looked as though it were made of thick gray smoke: the ghost of a spell.

"Deletrius!" Mr. Diggory shouted, and the smoky skull vanished in a wisp of smoke.

^{Harry Potter and the Goblet of Fire, Chapter 9, The Dark Mark}

We can assume that Dumbledore did removed the spells that in his mind might seem useful to Voldemort, except of course the spells casted in the Horcrux cave as he died shortly after.

Answer 5

There is a difference between the reversal spell and Priori Incantatem. The reversal spell (priori incantato) is used to show the previous spells cast by the wand it targets. Priori Incantatem is not a spell but an effect which happens when two wands with cores of the same animal clash. This happens with Harry and Voldy because they both have phoenix feather cores from the same phoenix, Fawkes.

So one does not perform a priori incantatem, it happens under very rare circumstances. It was this as an unintended consequence that killed Voldemort.

Answer 6

Voldemort does not have the full control over the Elder wand as he is not a killer of the former owner. Maybe some spells just did not work.