Particles following ところ （に, を, and で）

Question

• 料理をしているところに電話がかかってきて困った。
• デートをしているところを友だちに見られてしまった。
• 電車に乗ったところで今日は祝日だと気づいた。

In the above sentences, what decide the particle following ところ? They all seem to indicate a happening during/while the user is engaged in an activity.

Answer 1

As user4092 said, it is the verb that matters.

I will break down each sentence by explaining the verb.

Sentences

1. 料理をしているところに電話がかかってきて困った。

   電話がかかってくる accepts a number of things marked by に, and one of them is the time (compare: 「仕事中に電話がかかってきた。」).

   Thus, 料理をしているところ in this first sentence is functioning as a time.

2. デートをしているところを友だちに見られてしまった。

   Explaining this one is a little complicated since it's just a complicated sentence (using the adversarial passive), so you may want to come back to this after you know more Japanese, but anyways...

   _{Necessary tangent: 見られる is the passive of 見る. When you form a passive, you lift something from the underlying sentence to が, and the が-marked thing in the underlying sentence to に.}

   _{In this case, the original sentence is 友達が［（私が）デートをしているところ］を見た, and the 私が gets promoted to the が-marked thing of the passive, and of course 友達 becomes the に-marked thing:}

   _{友達が　　　［（私が）デートをしているところ］を　　　　　　　　　見た
   ⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓
   （私が）　　　　　　［デートをしているところ］を　　友達に　　見られた}

   So, the thing being marked by を is the thing being seen.

   As such, デートをしているところ here is not behaving like a time as in (1), but instead as a noun referring to a past event.

3. 電車に乗ったところで今日は祝日だと気づいた。

   Unlike (1), 気付く doesn't accept times in the に position.

   So, instead, 電車に乗ったところ here functions as a "location in time" where you did the realizing of 今日は祝日だ.

   Compare, 「電車に乗った時点で今日は祝日だと気づいた。」, where 〜時点 is another "location in time" sort of thing.

Summary

Basically, the complicated thing here is not ところ -- ところ is just flexible in terms of what it can behave as (time, location, noun) -- and that flexibility brings out the complexity of verbs in Japanese.

Being able to pick the right place to jam ところ with a verb more or less comes down having a good feeling for the verb and understanding what arguments it accepts.

Answer 2

It's the verb that counts.

1. A phone call came to the part where I am cooking.
2. My friend witnessed the part where I am going out.
3. I noticed today was a holiday at the part where I got on the train.

Answer 3

1. Just as / while I was cooking, the phone rang.

2. While I was in a date, I was seen by a friend.

However, をstress 「デートをしている」 as a direct complement, so literally, "the friend saw the fact I was in a date" .

3. While on the train, I noticed that today was a day off.

で stresses place here.

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If you want to understand them better as well as their translation, you should check subordinate sentences regarding grammar.