It's no secret that Horace Slughorn gave Voldemort information on making horcruxes, and a major thrust in the sixth book is Harry and Dumbledore trying to find out what Slughorn told him.

With that said, it seems like Voldemort already had a fair bit of information about horcruxes when he went to Slughorn. I'm slightly confused as to how the information Slughorn gave him actually helped him - it's not like Slughorn gave him an article on "how to make a Horcrux in 10 easy steps," and the majority of the things they discussed he already knew. And Slughorn never really answered Voldemort's question about how many horcruxes it's possible to make. That being said, how did Slughorn's information actually help Voldemort, and how was it enough information for him to actually make one?

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    You can make the second question into a separate post and get separate points for that one. But, I suspect the best answer will be "we don't know enough from canon sources, so the best we can do is speculate".
    – RichS
    Commented Mar 27, 2017 at 19:47
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    In point of fact, Horace didn't help Tom a whole lot. Tom was asking about what might happen if he were to attempt creating multiple Horcruxes, specifically the case of six Horcruxes (dividing one's soul into seven, a magically significant number). Horace was too horrified ("Merlin's beard, Tom!") to even contemplate the question seriously. However, the (intact) memory of that exchange was far more helpful to Tom's enemies (Albus and Harry), who then knew exactly what they were up against. It became something crucial to their eventual success in defeating the Dark Lord.
    – Deepak
    Commented Mar 28, 2017 at 7:34
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    @Deepak That can probably be added as an answer as well Commented Mar 28, 2017 at 20:07

3 Answers 3


Ron wondered this too, in Harry Potter and the Deathly Hallows:

"This is the one that gives explicit instructions on how to make a Horcrux. Secrets of the Darkest Art - it's a horrible book, really awful, full of evil magic. I wonder when Dumbledore removed it from the library... If he didn't do it until he became headmaster, I bet Voldemort got all the instruction he needed from here."
"Why did he need to ask Slughorn how to make a Horcrux, then, if he'd already read that?" asked Ron.
"He only approached Slughorn to find out what would happen if you split your soul into seven," said Harry. "Dumbledore was sure Riddle already knew how to make a Horcrux by the time he asked Slughorn about them. I think you're right, Hermione, that could easily have been where he got the information."
Harry Potter and the Deathly Hallows, chapter 6

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    Slughorn didn't exactly answer the question if I'm remembering correctly (correct me if I'm wrong) - did Voldemort work it out on his own or did he just decide to chance it? Commented Mar 27, 2017 at 20:28
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    As Slughorn didn't answer the question, I'll have to assume that, yes.
    – Mithical
    Commented Mar 27, 2017 at 20:30
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    So, Slughorn's information just confirmed what Voldemort already knew and wasn't actually particularly useful? Commented Mar 27, 2017 at 20:41
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    At the very least it's probably safe to assume that Slughorn wouldn't want a student to harm themselves, so while he didn't offer anything useful, he also didn't flag up that it was a problem, which may have been all the confirmation Riddle required.
    – delinear
    Commented Mar 28, 2017 at 8:44
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    @EJS - It was useful because it confirmed what he had previously suspected. Commented Mar 28, 2017 at 17:08

Mithrandir's answer already provides one relevant quote, but I'd say it lacks interpretation. What helped Tom Riddle was not so much what Slughorn said, but the two things he did not say:

  • Something like "no way, splitting a soul a second time leaves too little intact, it would destroy all soul pieces", possibly backed up by the story of someone mad enough to try and fail, would probably have stopped Tom from creating more than one Horcrux. Thus in hindsight Slughorn feels he made Voldemort more powerful by not preventing the creation of multiple Horcruxes instead of just one (which was bad enough).
  • And he did not say anything about Tom's rather disturbing question to anyone else. Had he been more suspicious, Riddle could have been stopped before he actually "became" Voldemort. Though I'm not sure he hadn't already created his diary by then.

So in a way Slughorn helped Voldemort by not not helping him.

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    This doesn't account for why Slughorn thinks the edited version of the memory (in which he gets angry and sends him away, but still does nothing) makes him look better.
    – Random832
    Commented Mar 29, 2017 at 14:20
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    @Random832 The simplest explanation could be that editing memories is too difficult, the more you change the easier it gets detected. Alternately, consider he could barely falsify his memory into one where he did tell on Riddle, which he obviously didn't. Not wanting anything to do with this Horcrux-Schmorcrux nonsense was probably just the most realistic performance he could give.
    – Zommuter
    Commented Mar 29, 2017 at 17:54

With thanks to @Mithrandir for his excellent answer and reference, as well as the discussion in the comments on his answer: it didn't help Voldemort in the least. Voldemort already knew how to make a horcrux - he wanted to know if he could make seven of them, and Slughorn apparently either didn't know or didn't care to share.

Given how ashamed he was of his memory of the discussion (as evinced by the fact that Harry had to manipulate him into giving him the information), Slughorn apparently believed he had given Voldemort significant information (or, at least, that he had missed the fact that his "theoretical discussion" with Voldemort wasn't so theoretical after all and that he had failed to take action), but the fact remains that his information wasn't what enabled Voldemort to make horcruxes.

It's unclear exactly how Voldemort found out that splitting his soul seven times would work. Possibly he worked it out himself somehow (or found it in a different book), and possibly he just chanced it and tried splitting his soul multiple times. Or, possibly, as pointed out in another answer, the fact that Slughorn objected that that would be a terrible thing to do (rather than an impossible thing to do) may have been enough to suggest to Voldemort that it was at least theoretically possible.

  • How are any new spells or potions discovered in the Potterverse? Commented Dec 2, 2022 at 4:54

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