My experience with grammar is it’s like that video of the baby that’s crying because his feet can’t touch the ground in the pool, but it’s actually just because he was leaned back and his mom pushes down his feet and he stands up and realizes it wasn’t nearly as bad as he felt.
Vocab is the mariana trench
EDIT: I found the video lol
It seems like the way the question is worded, that vocab is the obvious answer. Like, if I’m just being gifted with knowledge supernaturally, I’d 100% take vocab. Vocab is the number one reason I can’t understand something in Japanese. Learning grammar is achievable in a short amount of time, and honestly not that hard compared to other languages.
That said, for acquiring grammar vs vocab in the real world balance is needed. I’d say just crush through the 1000-2000 most commonly used words and some n5-n4 grammar real quick and let the information overlap between vocab and grammar as much as possible.
If you focus too much on vocabulary, you can end up in situations where you see sentences and know what each word means individually but not know what the sentence as a whole actually means. Can be very frustrating.
If you look at it objectively:
There are less than 1,000 grammar points to learn.
And the average high school graduate knows more than 24,000 words.
However, of the grammar points, only a couple hundred will see everyday use.
IMO the Pareto Principle (80/20) applies better to grammar than vocabulary. If you know 20% of the grammar, you know 80% of the everyday grammatical structure.
If you know 20% of the vocabulary, you know 20% of the words and have 20% of the expressiveness of a native.
The amount of vocab that WK teaches is well over the 80/20 rule, but ask anyone that’s completed level 60 if they would be able to understand jack smack if the only vocab they knew was the WK vocab they studied?
I am exactly the opposite. I would take vocab from a genie any day, because I have to hear and use a word about 50 times before it sticks, and there’s just so. much. vocab.
Edit: after reading through the rest of the thread I’m definitely not adding anything new, but in terms of magical, work free learning, vocab any day. Grammar is fun and easy for me (in particular) to study, but vocab is just such a slog. Real world, of course, you absolutely need both, the choice between learning one instead of the other is basically meaningless.
How about option 3? Can the genie give me perfect Japanese native pitch accent?
Haha! Good choice! Maybe try restarting life and be birthed by a Japanese woman in Japan, that might work 
To be fair, I guess the question was serious, but it was undermined by the ‘fun’ poll, which led people arguing about the silly hypotheticals 
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I picked grammar, not because I think I will have need to look up stuff with it as long as I will with words, but because grammar is harder to wrap my head around. Now that I’m more comfortably in intermediate, it isn’t so bad.
But if I’m having trouble with a sentence, it is never because of the words I have to look up, but because I can’t put together the puzzle pieces of grammar well enough to get the meaning.
Also, I would have answered this differently if Japanese was a language with grammar more similar to languages I already know (Swedish and English). If asked this about French, Italian, and Spanish which are three other languages I’m interested in acquiring, I would definitely answer vocabulary, because the grammar won’t be that different from what I already know.
But when it came to Japanese, I had to understand entirely different concepts. Just the use of passive and how prevalent it is. That there is a conjugation for making someone do something (and being made to do something). How saying must is done with a double negative. Just のに in general.
And how Japanese sentences are built in an entirely different way from the other two languages I know. Most of my difficulty still comes from not understanding how to take the building blocks of the sentences and their meaning and putting them together.
In contrast, looking up a word is easy, and doesn’t trip me up. So from that, I found that the more I master grammar, the more easily I read (my main reason for learning Japanese).
Japanese didn’t become available to me until I got solidly into intermediate grammar. I am not one of those people that just get it. I have friends (Swedes who know English well) who went to the Netherlands for a weekend, and by the end of the weekend, they felt like they could start to understand some Dutch. I’m not like that.
That is why for Japanese, I would pick grammar.
Now, if I could have a genie come with three wishes to master vocab or grammar for three other languages (I would probably pick French, Italian and Spanish as noted above, although maybe I’d switch one for German… 
), I’d probably pick vocab for all of them. Unless it was for a language I knew had grammar very different from Swedish, English, and Japanese. New concepts are much harder to learn than a new word. ^^
However, I would never suggest that my opinion applies to anyone else but me.
What we need here is more transitive vs intransitive verbs (it’s grammar related, no? 
), The role of を and why do we even have it, godan vs ichidan verbs and…
I’m sure I missed something.
Not really, part of why I say that is because there are certain ambiguities between them. に／へ are commonly presented as grammar but Joshi isn’t really grammar per se. In the sense that “is”, “a” and “are” are words(vocabulary), it is the rules for their use that is the grammar.
Without any traditional rules, it’d be pretty easy to surmise that the last character(s) before a new kanji in a sentence would be the place for these words.
I (topic) Tanaka (honorific) (direction of motion) flowers (direct object) give (*tense conjugation).
Deciphering meaning with enough vocabulary isn’t that unwieldy really. Probably makes construction difficult though.
well, I am at N2 on bunpro and honestly, so far less than 1% of grammar points in that level I have seen on dialogues in anime.
Since I am watching anime with japanese subtitles, I realize I need more vocab to understand more sentences. And if you know N4 and a little bit of N3, is completely enough to understand anime dialogues in its total.
Many points in N2 are archaic (as bunpro states in hints) or very formal, so where would I see them actually? Maybe politics or technical essay/dissertation?
I wll get to N1 eventually, because I have some spare time.
If you’re watching anime, that is basically 100% spoken Japanese. A lot of N2 grammar is not archaic or super-formal, but simply formal enough to be written grammar rather than spoken, and turns up in written material of all kinds. And quite a bit of it is spoken too (もんか、ばっかり、せっかく、せめて are a few that leapt out from a quick scan of an N2 grammar list.)
Dang, is that true? That’s actually pretty crazy!
I’ve found that N2 grammar turns up all the time when reading tbh, and I’ve not been reading politics or essays or anything like that. I did some N2 grammar study the other day, studied 6 grammar points, and then three of them (that were marked as formal in the textbook) turned up in the chapter of sports manga I read that afternoon (specifically, they were grammar points often used in announcements etc, so maybe does make more sense for them to turn up in a sports manga). Reading novels (again, I’ve not read anything super formal or technical) and playing video games I’ve also found N2 grammar coming up again and again (fire emblem three houses in particular loves to use N2 grammar).
Of course, a lot of the time N2 grammar is kind of just adding extra nuance to something that you could probably decently understand with N3 grammar so I don’t think it’s really a blocker, but I definitely wouldn’t say that N2 grammar points are at all rare or limited to formal materials.
Also, note that “archaic” doesn’t mean “only seen in old sources and things quoting them” – it’s more “was common in the past, but now much less common, and now is more likely to survive in fixed phrases or usages or in text wanting to give a historical feel”. For instance the -ぬ suffix is archaic in the sense that modern Japanese doesn’t customarily negate verbs that way any more, but it still appears in modern texts, which is why it’s in N2. (Indeed, in the thread where somebody is working through the Chainsaw Man manga you’ll find a character who has a speech habit of using -ぬ, and that sort of character turns up in anime too.) Everything in N2 is there because it really does turn up – it’s just that compared to N3 and lower grammar it’s less frequent, which is why it gets taught later.
Yup, N2 grammar points definitely do show up not only in anime and manga, but also in games for teens. I’m playing Knights Chronicle on mobile and even though it’s mostly casual and/or spoken Japanese, N2 grammar is kinda common.
I think where one might not see much of it is regular shounen anime, but for younger audiences.
Nah, I’d ask the genie for grammar! These days it’s pretty easy to look up words in a dictionary app and there are soooo many SRS/flashcard resources for memorizing vocab. But having the complicated grammar right away (especially if it includes all the politeness rules) means you can talk with other people better and also jump into more advanced reading material.
(In the real world of course you learn both as you go along and spend more “formal” study time on whichever one is holding you back at the moment.)
I completely agree. Especially if you read medieval-ish fantasy, things like ぬ are bound to show up.
I think べき is a great example of “archaic” things that can still be in common use. べき (N3) itself is common of course, but its other forms less so. There’s べからず (N1), べく(N1), and べし (not sure, but probably N1). I’ve probably seen them all in their “standalone” forms (not set phrases) when reading, but there’s also set phrases/words like なるべく (really common) or 恐るべき・恐るべし (not super common, but appears from time to time).
Also, when just reading a chapter of a slice of life, modern day manga I found two set phrase “archaic” grammar points. The first was 仲良し. This is super common, probably even a lot of beginners have seen it, but it’s based on an archaic conjugation of 良い to get 良し. The second was 予期せぬ, a set phrase using ぬ to get せぬ instead of the more modern しない.
Maybe you are taking a more practical (hypothetical) situation. I think you can get a decent grasp of grammar patterns in a pretty short time-frame, like a year, whereas accumulating a sizeable vocab base can take at least ten times that. After the initial grammar, vocab is pretty much always the bottle-neck that limits what content you can consume. Having that at the start would be an incredible kickstart to acquire grammar. You can extrapolate meaning from known words a lot easier, the other way it’s pretty hard.
By the way, how do you define grammar? I can understand/communicate basic Spanish but have never read a grammar explanation in my life. Would you count that as ‘knowing grammar’? Are particles words or grammar? This is all pretty vague so I guess this is a pretty pointless discussion 
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Honestly, your post sounded a bit condescending, so I wasn’t sure if I should answer. Or maybe I just misread the tone.