In the Harry Potter universe, magically inclined children are sent to school where they start learning how to cast spells and other magic related activities. It's clearly shown that the children have to learn how to do things.

But in The Halfblood Prince, Harry casts a spell without knowing what it does by just saying the word. I've never been able to understand how this is possible. This would imply that spells don't need understanding, you just need to utter the words (like in Eragon).

Does anyone have any canonic reference as to how this is possible? Or a likely explanation.

  • 3
    Hard to believe that the spells tag has not been created yet!
    – JohnP
    Apr 23, 2011 at 9:50
  • 5
    Kind of a chicken and egg problem - how did the first spell ever get cast...?
    – TGnat
    Apr 23, 2011 at 13:13
  • @TGnat how indeed. Maybe it got handed down by creatures with natural affinity to magic?
    – JohnP
    Apr 24, 2011 at 4:42
  • @TGnat That answer depends on whether you're a creationist wizard or a scientific one.
    – Prometheus
    Jul 20, 2020 at 18:36

4 Answers 4


First of all, let me say that there seems to be 3 main traits to casting a spell. First the words and then secondly, the right wand motion. Lastly, concentration. If all 3 are achieved, the spell is cast. There are some spells where you have to know exactly what's going to happen, it's true (Think Accio, the summoning spell), but there are others where it doesn't seem to be as important (Like Lumos, the light spell)

Secondly, this is a pretty common trait among many skills. It's hard to learn the basics, but once you learn the basics, you can learn the advanced skills pretty easy. It's because Harry had been studying for so long that he was able to pick up new spells fairly easy.

Also, there are many examples of Harry learning new spells from books, and other wizards. In particular, take a look at Goblet of Fire. You'll see a lot of spell learning from books. Granted, there was somewhat of an idea as to what was going to happen, but... And, even if Harry doesn't know exactly what the spells will do from Half Blood Prince, he at least has an idea.

Lastly, there are many examples of wizards casting spells not realizing what they will do, especially underage wizards. Granted they just will it to happen, without words, but it still can happen.

  • 5
    mutliple times in the series people are seen casting spells without a wand and/or a verbal component. concentration is probably the only requirement to casting a spell. in the beginning the wand movements and words are probably there to create a magical "true word" of the outcome of the spell and later on they aid the caster in maintaining concentration while casting. this way, spell research would be possible by combining various words and wand motions to create new spells (forming new true words). but this all just my speculation.
    – Xantec
    Apr 24, 2011 at 3:52
  • 1
    Hmm, that has merit. Could be that the initial stages are required to increase your affinity to magic or the magical force. And later on you can do it by feel. But the thing here was, Harry didn't know the wand motion nor the action. He spoke the words and the appropriate spell occurred. Like you mentioned, spells are probably a combination of all three factors with all of them being optional to varying degrees. That would explain it. Thanks for the reply!
    – JohnP
    Apr 24, 2011 at 4:41
  • 1
    I think it would have been fascinating to have a mute or handless wizard in official continuity -- Rowling could have explored exactly how much magic is achievable without a wand and/or speech. Jan 18, 2012 at 21:37
  • Just wanted to add that, if I'm correct and the OP did mean Imperius and Crucio, then Harry learned it from observing it happening/reading about its effects, If I'm correct, during not-so-Moody's classes, and Other tortures (Umbridge If I'm not mistaken), as Pearson mentioned, it takes knowing the effects and having the right disposition, for example, for crucio (when Harry tries to use it on Bellatrix) he's told that he can't use it because he has no desire to actually torture someone at the degree that Crucio does
    – Oak
    May 3, 2014 at 10:55
  • I was under the impression you don't necessarily need wands to cast spells since there is wandless casting. Mar 22, 2017 at 16:56

First, I think it's important to consider that J.K. Rowling has inconsistencies throughout her series that sometimes simply cannot be explained; these are called "Flints", after the Slytherin student Marcus Flint, who accidentally appeared in two of the books as a seventh year twice in a row. J.K. Rowling later acknowledged that this was due to her own error, and it was not caught by her editors. There are numerous instances of seeming canon inconsistency in the Harry Potter series, just as an FYI, not as an insult or a slight toward the series. I'm pointing this out because I think there may not be a perfectly conclusive answer to this question. I interpret the answer as complex and layered. Canon examples follow.

Magic is an elemental, fundamental, and learned skill. There are numerous components involved in properly channeling it and "making it work". There are three types of spells in Potterverse (from jkrowling.com):

"Every now and then somebody asks me for the difference between a spell, a charm and a hex. Within the Potter world, the boundaries are flexible, and I imagine that wizards may have their own ideas. Hermione-ish, however, I've always had a working theory."

Spell: The generic term for a piece of magic.

Charm: Does not fundamentally alter the properties of the subject of the spell, but adds, or changes, properties. Turning a teacup into a rat would be a spell, whereas making a teacup dance would be a charm. The grey area comes with things like 'Stunning Spells', which on balance I think are Charms, but which I call spells for alliterative effect.

Hexes: Has a connotation of dark magic, as do jinxes, but of a minor sort. I see 'hex' as slightly worse. I usually use 'jinx' for spells whose effects are irritating but amusing.

Curses: Reserved for the worst kinds of dark magic. JK Rowling - jkrowling.com

Foremost, a child must be born with inherent magical ability; it cannot be learned by Muggles or Squibs, who lack the proper genetic abilities to produce magic. It is noted throughout the series that magical children have the ability to "make things happen', as Hagrid says, when they are scared, angry, or afraid (i.e. accidental magic). Examples of accidental magic include Harry's hair growing back overnight after Petunia Dursley cuts it to the scalp (SS/PS), Harry finding himself on top of his school cafeteria's roof while running from his cousin Dudley Dursley and Dudley's gang pre-Hogwarts (SS/PS), making the wrong-sized clothes fit (PP/SS), and blowing up his Aunt Marge like a balloon when angry (POA).

So, to cast spells at all, magical abilities must exist. It's clear from canon that different witches and wizards develop their magical skills at different paces, some being more prodigious than others. For example, at age eleven, we have Tom Riddle, who was previous unaware that what he possesses is called magic, but who is already channeling it without using a wand or incantations: In Half-Blood Prince, when Dumbledore meets Tom Riddle for the first time, Tom Riddle is excited to learn that he is indeed "special" (magical) and reveals to Dumbledore:

"I can make things move without touching them. I can make animals do what I want them to do without training them. I can make bad things happen to people who annoy me. I can make them hurt if I want to." (Tom Riddle -- Half-Blood Prince -- Chapter 13)

As well, Neville Longbottom laments that his family thought he was a Squib until he fell outside his house and bounced down the path, showing his first inklings of magic (SS/PS). In Chamber of Secrets, Hogwarts caretaker Argus Filch, who we learn is a Squib, trying to learn magic via Kwikspell mail-order study guides; he is unsuccessful in learning magic, as demonstrated in Half-Blood Prince, where Hermione notes that Filch is a poor wizard and cannot discern potions or poisons from regular concoctions, such as perfume or oak-matured meade.

Canon demonstrates that, at the very least, there must be a fundamental understanding of magic for spells to work. Yet, practice is also required -- technique matters. Pronunciation of the spell matters. As well, magic seems to react differently to individuals based on character and skill. Finally, the emotion a witch or wizard puts into casting a spell seems to affect the caster's ability to succeed. Note the following canon references:


"Now, don't forget that nice wrist movement we've been practicing!" squeaked Professor Flitwick, perched on top of his pile of books as usual. "Swish and flick, remember, swish and flick. And saying the magic words properly is very important too -- never forget Wizard Baruffio, who said 's' instead of 'f' and found himself on the floor with a buffalo on his chest."

It was very difficult. (Sorcerer's Stone -- Chapter 10)


"The spell I am going to try and teach you is highly advanced magic, Harry -- well beyond Ordinary Wizarding Level. It is called the Patronus Charm [. . . .] But I must warn you, Harry, that the charm might be too advanced for you. Many qualified wizards have difficulty with it." (Remus Lupin - Prisoner of Azkaban -- Chapter 12)

"Harry, I can't believe it. . . . You conjured up a Patronus that drove away all those Dementors! That's very, very advanced magic. . . . " (Hermione Granger -- Prisoner of Azkaban -- Chapter 21)

"Impressive," said Madam Bones, staring down at [Harry], "a true Patronus at [fifteen years old] . . . very impressive indeed." (Amelia Bones -- Order of the Phoenix -- Chapter 8)

Regarding Slughorn's lunch on the Hogwarts Express in Half-Blood Prince, where Slughorn invites students he sees as special to eat with him, Harry asks Ginny Weasley:

"How come you ended up in there, Ginny?"

"He saw me hex Zacharias Smith [. . . .] When Slughorn came in, I thought I was going to get detention, but he just thought it was a really good hex and invited me to lunch. Mad, eh?" (Ginny Weasley -- Half-Blood Prince -- Chapter 7)

"Yes, those who progress to using magic without shouting incantations gain an element of surprise in their spell-casting. Not all wizards can do this, of course; it is a question of concentration and mind power which some" -- his gaze lingered maliciously upon Harry once more -- "lack." (Severus Snape -- Half-Blood Prince -- Chapter 9)

Numerous instances of Hermione Granger mastering magic through sheer determination, study, and practice are present throughout all seven books.


"Never used an Unforgivable Curse before, have you, boy?" [Bellatrix] yelled. She had abandoned her baby voice now. "You need to mean them, Potter! You need to really want to cause pain -- to enjoy it -- righteous anger won't hurt me for long -- I'll show you how it is done, shall I? I'll give you a lesson--" (Bellatrix Lestrange -- Order of the Phoenix -- Chapter 36)

"Avada Kedavra's a curse that needs a powerful bit of magic behind it -- you could all get your wands out now and point them at me and say the words, and I doubt I'd get so much as a nosebleed." (Mad-Eye Moody -- Goblet of Fire -- Chapter 14)

In Deathly Hallows, Harry casts the Imperius Curse, an Unforgivable Curse, on a Gringotts goblin and the Death Eater Travers as the trio tries to break into Gringotts to steal the Hufflepuff cup Horcrux, having never cast the spell before. He was under extreme duress in the situation, with Hermione as Bellatrix being suspected as an imposter upon trying to gain access to the Lestranges' vault. He was able to successfully cast Imperio even while using Draco Malfoy's wand. However, Harry does worry whether he cast Imperio "strongly enough". In total, Harry uses the Imperius Curse four times while in Gringotts.


"The Imperius Curse can be fought, and I'll be teaching you how, but it takes real strength of character, and not everyone's got it." (Mad-Eye Moody -- Goblet of Fire -- Chapter 14)

"First of all, Harry, I want to thank you," said Dumbledore, eyes twinkling again. "You must have shown me real loyalty down in the Chamber. Nothing but that could have called Fawkes to you." (Albus Dumbledore -- Chamber of Secrets -- Chapter 18)

"It is our choices, Harry, that show what we truly are, far more than our abilities." (Albus Dumbledore -- Chamber of Secrets -- Chapter 18)

Mr. Ollivander says in Deathly Hallows, "Oh yes, if you are any wizard at all you will be able to channel your magic through almost any instrument. The best results, however, must always come where there is the strongest affinity between wizard and wand. These connections are complex. An initial attraction, and then a mutual quest for experience, the wand learning from the wizard, the wizard from the wand." (Ollivander -- Deathly Hallows -- Chapter 24)

In Half-Blood Prince, Harry is able to cast Sectumsempra on Draco Malfoy without knowing what its exact effects would be; however, he was aware that Sectumsempra was "for enemies", and Harry carries strong negative emotions for Draco Malfoy throughout the series. Harry's emotions helped him to channel Sectumsempra properly against Malfoy, even though he wasn't fully aware of what Sectumsempra would do.

Also in Half-Blood Prince, Harry is seen casually experimenting with Levicorpus, which hoists Ron up into the air as if Ron's being held upside down by the ankle. Little effort seems to be required to perform this seemingly harmless jinx.

As J.K. Rowling has provided a spell tier, it would make sense that the severity of the spell, combined with the witch's or wizard's basic training, inherent magical abilities, character, and emotional state all come together to produce an act of magic. The logistics are complex and variable.

  • +1 great answer! I guess what we can take away from it is that several factors would go into making a spell a spell. And here people thought magic was the easy way out :D
    – JohnP
    Nov 23, 2011 at 17:52
  • @JohnP -- Thanks! Glad you found it informative and that it made sense :) -- Nov 23, 2011 at 22:06

I've examined magic from many different sources and the magic of Harry Potter's world fits into most of the general rules, though there are a few special cases which could explain other effects.

The primary requirement in most cases is that the caster be able to access and focus magical energies.

When casting, the caster only really needs to desire and have belief that the effect will occur. If there is doubt or lack of desire the spell will either be weak or will fail.

Everything else is a focus, they help the caster envision the desired effect: Words - Words are one of the most powerful of foci. Words are a natural way to describe a desire and words for spells are often chosen for how well they represent the spell. In practice, you can associate any word with a spell, but using the word 'pyro' as a focus for a water creation spell would cause dissonance if the caster knew the meaning for pyro. Why use a foreign language? It's not necessarily that the language is magical (though this is a potential, see the special cases below), it's more of a safety. If a caster used his native language when casting spells, got irritated at someone and blurted out "Just die already!" he could accidentally kill the target of his ire.

Motion - This may not only be wand waving, but can also include position and movement of the rest of the body. Again, the movement should reinforce the idea of the effect.

Components - In many systems, a component is consumed in the casting, but this is not always true. Casting aids are components that can be used repeatedly and this is what the wands are.

Wands - Wands can help in multiple ways, depending on how they are crafted. At the most basic, they can be used to enhance the movement effect and thereby enhance the forming of the spell. But for casters learning the craft, a wand that provided a buffer would be highly desired. This would prevent accidents from affecting the caster (Like Ron's broken wand did with the slugs). A learner may also need help drawing the energies, and a wand could help with that also. So why do they continue to use wands when they become accomplished casters? On the practical side, it's a buffer and a power enhancer. It is also a symbol that they are casters. Lastly, like any focus, it can become a crutch. The caster may come to believe that he cannot cast spells without using it.

Special Cases: In some worlds, some words do have power. In effect, they become untethered enchantments waiting for someone to use them. But in order to use one of these words you have to use it correctly and with correct pronunciation. However, for Sectumsempra, or any spell, to gain such a status, it would have to be used a lot, or used to enchant a location.

Sources used: Harry Potter series, Wheel of Time series, Midkemia series, Dungeons & Dragons, Rolemaster, Rifts, and more.

  • This is a great answer !
    – JohnP
    May 3, 2013 at 11:30

I always thought that Harry seemed to learn from the Half-Blood Prince better than he did from other sources. Accio is one example; Harry struggles very hard in Book 4 when mastering that spell. On the other hand, Levicorpus, from the HBP's Potions book in Book 6, comes to him effortlessly even though he's never been able to do a spell nonverbally before that point. There's probably a difference in power between these two spells, but pretty much everything about the book benefits Harry, right up until he uses Sectumsempra on Malfoy and Snape is the first on the scene.

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