How could Hermione have gotten more OWLs than classes?

Question

I was doing some research for this question, and that brought to my attention something that doesn't add up.

According to Half-Blood Prince, Hermione achieved eleven OWLs:

'Oh, come off it,' said Ron, striding over to her and whipping her results out of her hand. 'Yep - ten "Outstandings" and one "Exceeds Expectations" in Defence Against the Dark Arts.'

^{_{Half-Blood Prince Chapter 5: "An Excess of Phlegm"}}

According to Pottermore, there are twelve OWL subjects:

1. Transfiguration
2. Charms
3. Potions
4. History of Magic
5. Defence Against the Dark Arts
6. Astronomy
7. Herbology
8. Arithmancy
9. Muggle Studies
10. Divination
11. Study of Ancient Runes
12. Care of Magical Creatures

Of these, Hermione was taking ten in fifth year: she dramatically drops Divination about midway through Prisoner of Azkaban, and she says at the end of that book that she dropped Muggle Studies.

We can confirm this number, since Harry's OWL results (And complete class list) is printed earlier in the chapter: he's taking nine courses. We know Hermione is taking Ancient Runes and Arithmancy (She frets about how she screwed up the exams for those courses earlier still), and she's not taking Divination; otherwise, their classes are identical.

So how did she get eleven OWLs? I could accept that she'd be able to write the exam without taking the class (And pass with flying colours; it is Hermione, after all), and for Muggle Studies I'd take that as valid, but it seems like something she'd dismiss as being "Too easy" - the reason she dropped the course in the first place.

Honestly I suspect the answer comes down to "JKR sucks at math", but I was curious if this had ever been addressed in canon.

Answer 1

Where, exactly, does it say that she got twelve O.W.L.s?

This is what my copy of Half-Blood Prince says:

“Oh, come off it,” said Ron, striding over to [Hermione] and whipping her results out of her hand. “Yep – nine “Outstandings” and one “Exceeds Expectations” in Defence Against the Dark Arts.” He looked down at her, half-amused, half-exasperated. “You’re actually disappointed, aren’t you?”

That makes ten OWLs, which is entirely consistent with the known subject list.

---

It seems I might have spoken too soon. I’m using a fairly recent British edition of the book, but other printings (including the OP’s – see comments) disagree. The HP Wiki article on O.W.L.’s states:

In early editions of Harry Potter and the Half-Blood Prince, Hermione Granger is said to receive eleven O.W.L.s, scoring ten O's and one E. However, after the events of Harry Potter and the Prisoner of Azkaban, Hermione shrunk her class load from twelve subjects to ten, dropping both Divination and Muggle Studies. This was corrected in the Scholastic edition, where Ron instead states the she received nine O's and one E, giving her a total of ten O.W.L.s.

This version of events is backed up by the following article:

Publishers have been forced to correct an error in one of JK Rowling's Harry Potter blockbusters.

The hardback edition of the sixth instalment of the schoolboy wizard's adventures, Harry Potter and the Half-Blood Prince, said that swotty Hermione Granger had scooped 11 top results in her Ordinary Wizarding Levels (OWLs). But hawk-eyed readers spotted that in the previous book, Harry Potter and the Order of the Phoenix, she had only taken 10 subjects.

Publishers quickly fixed the discrepancy in the next edition, downgrading her results from one "Exceeds Expectations" and ten "Outstanding" grades to nine "Outstandings" and one "Exceeds Expectations".

The change in the Harry Potter books was reported on fan site www.mugglenet.com.

A spokeswoman for publishers Bloomsbury said that the error had been spotted last year and quickly fixed.

"In book six it said 11 and book five it said 10," she explained.

"It was corrected immediately."

_{("Potter Book's OWL-ing Error Fixed", The Yorkshire Post, 2nd September 2006).}

This in turn seems consistent with my and the OP’s experience. Chalk this one up to JKR’s dodgy maths.

Answer 2

Ok so JKR was right and there are 11 O.W.L.s. Allow me to explain...

Okay so first you need to take into account all the subjects taught at Hogwarts:

1. Transfiguration
2. Charms
3. Potions
4. History of Magic
5. Defence Against the Dark Arts
6. Astronomy
7. Herbology
8. Arithmancy
9. Muggle Studies
10. Divination
11. Study of Ancient Runes
12. Care of Magical Creatures
13. Alchemy

Alchemy is stated as an official optional subject at Hogwarts.

There are 13 subjects that Hermione had taken at the start of the 3rd year or something, listed above.

She quit Muggle Studies and Divination: 13 - 2 = 11, as JKR said.

1. Transfiguration : O
2. Charms : O
3. Potions : O
4. History of Magic : O
5. Defence Against the Dark Arts : E
6. Astronomy : O
7. Herbology : O
8. Arithmancy : O
9. Muggle Studies : QUIT
10. Divination : QUIT
11. Study of Ancient Runes : O
12. Care of Magical Creatures : O
13. Alchemy : O

'Oh, come off it,' said Ron, striding over to her and whipping her results out of her hand. 'Yep - ten "Outstanding" and one "Exceeds Expectations" in Defence Against the Dark Arts.'