I just discovered this. It seems like we’re in for a good time. :)

https://nihongoichiban.com/home/japanese-grammar-particles/

Anyway, although I’m really not an expert, I think I can provide a little more in-depth answer about the use of を in your particular example. The answer I would have expected Joel to give, actually, since he always explains things so well. I guess he didn’t want to get too technical, but I don’t think I will either.

You have two things to remember, here (if you don’t already know them):
-を marks the direct object of a verb.
-The direct object is a noun phrase that answers the question “What?”.

Ex:

I drove the car.
“To drive” is the verb. What did you drive? The car. “The car” is direct object. So を is required.

I drove to London.
“To drive” is the verb. What did you drive? We don’t know. “To London” doesn’t answer that question. It is not direct object so you won’t use を.

As for the sentence you’re asking about.

“To open” is the verb. What did you open ? The door. “The door” is direct object, which justifies the use of を.

Please note that this doesn’t work with linking verbs such as “to be”, which have a complement instead of an object. A complement is used for renaming or describing the subject, as in “This weird tool is a foot slide.” or “He is a nice guy.”

I can’t say much about に, though. Especially since, as Joel implied, へ seems to be the one to go to in some situations involving movement, and there are some other situations where に is used that really don’t involve movement unless you try very hard to make said situation fit in the box with a lot of approximations and convoluted reasoning, which are okay for vocabulary mnemonics, but really not as good for grammar.

Hope this helped a bit.

Cheers!

See? I knew you were getting tired of my questions. You’re starting answering them even before I ask them.

Joel wrote:

へ and に have similar meanings, but に tends to put more emphasis on the destination, while へ puts more emphasis on the movement itself.

Replace the period with a question mark, and that’s pretty much what my next question was going to be. Plus, you exceed my expectations by pointing out useful stuff like this particular use of を, or this “surface” meaning of に which I was quite not getting.

Thanks.

Last time I checked, Koichi forgot to include a lesson on へ (just something that slipped between the cracks, unfortunately). On the plus side, though, unlike the thousand uses for に, what’s mentioned above pretty much covers everything you need to know about it, except for the fact that when it’s functioning as a particle, it’s pronounced え.

If I may give my uptake on the matter…

In English, yes, it is direct object, because “to enter” is transitive (“direct”, although I’m not sure if this is a thing in English). But that’s not how you should see it in Japanese. If you followed this logic, then you should also write スーパー　を　はいりました, which you don’t.

You’d write スーパー　に　はいりました because はいる is intransitive – meaning it never takes an object, direct or indirect – and because に is the particle used for the point of arrival (#30 in the list).

I think the を in your sentence should be understood as the point-of-departure を (#28).

I believe it makes sense, and I trust Joel will correct me if I said anything wrong anyway. :)

That’s one big thing you have to be wary about when you a learn a language, in my opinion: verbs transitivity.