What's the difference between 公園を散歩する and 公園で犬を散歩させる?


Normally we say 公園を散歩する because 散歩する is a verb that expresses movement in
space, and is thus followed by を, which also expresses movement in space.

But if the verb is changed into 犬を散歩させる, in this situation, why is で added to
公園, rather than を? As I often see expressions like: 公園内で犬の散歩をすることは禁止していません.

I think both 犬の散歩をする/犬を散歩させる and 散歩する express movement in space, then why
don't we use 公園を in the condition of 犬の散歩をする/犬を散歩させる?

If it's okay to use 公園を犬の散歩をする/犬を散歩させる,then why do so many people choose to
say 公園で? What are the differences between them? I would really appreciate it
if you could give me a detailed answer of this problem!!!




As a prerequisite, you need to understand these two points:

  * When a causative construction (～させる) is involved, the agent (causee) is marked with either を or に depending on the type of the verb. See [this question](https://japanese.stackexchange.com/q/33510/5010).
  * Some intransitive motion verbs are tricky and may or may not take を. When the purpose of the action is irrelevant to traveling, で is chosen. For example, プールを泳ぐ is used in the context of competitive swimming where a swimmer travels from one end of the pool to the other, but プールで泳ぐ is used when you are recreationally swimming in the pool. See [this question](https://japanese.stackexchange.com/q/98290/5010). 公園で散歩する is much less common than 公園を散歩する, but it's not necessarily wrong.

With these in mind, there are three possible causative expressions about 犬の散歩.

  1. 犬 **を** 散歩させる: When the place is completely irrelevant, this is perfectly fine.
  2. 犬 **に** 公園 **を** 散歩させる: When you add 公園を to the verb, suddenly you must mark 犬 with に instead of を. This is a grammar rule. 犬を公園を散歩させる is grammatically wrong.
  3. 公園 **で** 犬 **を** 散歩させる: But this is also fine.

There is a slight difference between sentences 2 and 3. Usually, if you want
to say "walk the dog in the park", Sentence 3 sounds more natural. I guess
this is because the act of "walking the dog" is for the dog's recreational
purposes rather than for traveling. Sentence 2 sounds like you are taking the
dog's collar off and letting it walk in the park at its own will.

