Learn Hardcore Japanese: yama de kudamono wo tabemasita.

In this sentence, で marks the location where the action takes place. So 山で means “at/on the mountain.” It tells us you ate fruit while you were on the mountain.

Why is を used after 果物?

を is the object‐marking particle. It indicates that 果物 (fruit) is what you ate. Without を, the sentence wouldn’t clearly show the direct object of the verb 食べました.

Why isn’t there a subject like “I” or “we” in the sentence?

Japanese often omits the subject when it’s clear from context. Here, it’s understood that you (the speaker) ate fruit. In Japanese, you don’t need to say 私が unless you want to emphasize the subject.

What tense and level of politeness is 食べました?

食べました is the past tense, polite form of 食べる (“to eat”). It shows that the action happened already, and the speaker is using a polite style (the “‐ました” ending).

Could I use 山に果物を食べました instead of 山で?

No. に marks a point of arrival or existence, not the place of action. Saying 山に果物を食べました sounds like “I ate the fruit to the mountain,” which is ungrammatical. For location of an action, you need で.

Can I replace 山 with another place?

Yes. Any location where an action happens uses で. For example, 公園で果物を食べました (“I ate fruit in the park”) or 家で果物を食べました (“I ate fruit at home”).

Why is the word order 山で果物を食べました and not 果物を山で食べました?

Both orders are grammatically correct. Japanese word order is flexible. Putting 果物を first shifts emphasis onto the fruit; starting with 山で emphasizes the location. The usual default is “location – object – verb.”

How would I say this sentence more casually?

In casual speech, you can use the plain past form 食べた instead of 食べました:
“山で果物を食べた。”

Is 果物 singular or plural here?

Japanese nouns generally don’t mark singular vs. plural. 果物を食べました could mean “I ate a piece of fruit” or “I ate some fruit,” depending on context. If you want to specify quantity, you’d add a counter (e.g. りんごを二つ食べました).

Can I drop particles like で or を in casual speech?

Dropping particles can happen in very casual conversation, but it can lead to ambiguity. In writing or polite speech, it’s best to keep で and を:
“山で果物を食べた” (casual, still clear) rather than “山　果物　食べた,” which feels incomplete.