How did Voldemort know about the magic of Lily's sacrifice?

Question

Related: Why did Lily's enchantments work for Voldemort?

MA: Did [Lily] know anything about the possible effect of standing in front of Harry?

JKR: No – because as I’ve tried to make clear in the series, it never happened before. No one ever survived before. And no one, therefore, knew that¹ could happen.

MA: So no one – Voldemort or anyone using Avada Kedavra – ever gave someone a choice and then they took that option [to die] -

JKR: They may have been given a choice, but not in that particular way.

_{J.K. Rowling's Exclusive Interview with Mugglenet -- Part One -- with Emerson Spartz of Mugglenet and Melissa Anelli of The Leaky Cauldron.}

Voldemort counters J.K. Rowling with:

‘You all know that on the night I lost my powers and my body, I tried to kill him. His mother died in the attempt to save him – and unwittingly provided him with a protection I admit I had not foreseen ... I could not touch the boy.’ Voldemort raised one of his long white fingers, and put it very close to Harry’s cheek.

‘His mother left upon him the traces of her sacrifice ... this is old magic, I should have remembered it, I was foolish to overlook it ... but no matter. I can touch him now.’

_{Goblet of Fire - page 566 - Bloomsbury - chapter thirty-three, The Death Eaters}

So how did Voldemort know about the magic invoked by a mother who dies, with love, for her child if it never happened before?

¹<sub>"that could happen" means someone could survive Avada Kedavra if his/her mother chose to sacrifice her life instead of stepping aside and letting her child be killed. At least that's the definition that I read within context of the quote.

I'm looking for an answer grounded in canon -- the books, Pottermore, or JKR interviews or writings are all fine, as are subjective answers within the spirit of canon. Thanks!</sub>

Answer 1

I don't think this is a contradiction.

In Order of the Phoenix, Dumbledore explains Voldemort's knowledge and power:

I knew that Voldemort’s knowledge of magic is perhaps more extensive than any wizard alive. I knew that even my most complex and powerful protective spells and charms were unlikely to be invincible if he ever returned to full power.

But I knew, too, where Voldemort was weak. And so I made my decision. You would be protected by an ancient magic of which he knows, which he despises, and which he has always, therefore, underestimated – to his cost. I am speaking, of course, of the fact that your mother died to save you. She gave you a lingering protection he never expected, a protection that flows in your veins to this day.

There are several places he could have heard of it: Dumbledore, his spies in the Department of Mysteries, or while studying advanced Dark Magic.

However, in an FAQ on her website, JK Rowling stressed that this was not an uncharted area of magic:

What exactly happened when Voldemort used the Avada Kedavra curse on Harry in the forest?

Again, Voldemort violated deep laws of magic he did not understand, but there is more to it than that. […] It is important to state that I always saw these kinds of magic (the very deepest life and death issues) as essentially un-scientific; in other words, there is no “Elder Wand + Lily’s Blood = Assured Survival” formula.

This fits with your assumption that JK Rowling is referring to the specific incident as unpredictable.

Voldemort also had Barty Crouch Jr. as his spy in Hogwarts. Dumbledore seems to trust Moody, and by Deathly Hallows, he'd told the real Moody about Harry's protection. It's quite possible Crouch gave Voldemort the details, and they planned his resurrection accordingly.

So by the time of the graveyard scene, Voldemort definitely knew that love was potentially a powerful protective charm. He may even have known the specifics of Harry's case. This alone may justify his speech in the graveyard.

But Voldemort isn't compelled to be honest with his Death Eaters. His priority is rallying support, and convincing them that he's still worth their faith after 14 years away.

Did Voldemort know that Lily's sacrifice would save Harry? Probably not (or he'd never have given her the choice). But the Death Eaters don't know that.

Instead, I think his speech is probably boasting for his Death Eaters. By claiming knowledge of what defeated him last time, he appears more powerful and intimidating. It also makes Harry seem weak. There was nothing special or powerful about him; it was just his mother who saved him, and now she's dead.

This would be a contradiction if we could trust Voldemort's word, but I don't think we can.

Answer 2

I don't have canon proof but I think the explanation is simpler than what Alex gave.

As usual, JKR's wording is very vague and imprecise and THAT accounts for your perceived contradiction.

"And no one, therefore, knew that could happen" means that "nobody knew the person could survive Avada Kedavra".

Voldemort (and in different quote supplied by Alex, Dumbledore refers to it), in turn, was talking in general about "love protection magic" which he knew of and about. What he did NOT know was that the magic would specifically behave in a specific way (rebound Avada Kedavra) - and likely, didn't even consider that this magic would be triggered by Lily's sacrifice since he dismissed it as unimportant.

So there's no contradiction.

• Voldemort knew about the magic as a concept. Dumbledore's quote in OotP confirms that.
• Voldemort likely didn't consider he'd be triggering it when he killed Lily.
• As such, he didn't check baby Harry for traces of it
• He definitely didn't know that the magic's effect would rebound his AK on him.
• But, upon further reflection, he figured it out by GoF time as the reason for his failure, AND was able to detect the magic traces on Harry once he knew to look for them. Hindsight, as they say, us 20/20.