I came across the sentence その子は指で十数えました in writing, and I was under the impression that, in written Japanese particles are not omitted. I can see that that sentence means, "That child counted to ten with her fingers". However, I'm having difficulty understanding if there should be an を (or another particle) after 十. I feel like 十 should be the direct object of 数えました, but maybe my understanding of the verb 数えました is incorrect. Could someone help me further understand this sentence?
No particle is omitted in this sentence. We rarely say 十を数える regardless of it's written or spoken, in the first place. This 十 is like an adverb that directly modify a verb without any particle, and this happens very often.
By the way, this 十 can be read as じゅう and とお, both of which are fine but the former is common.
Here are some formal ways to use 数える:
- 五【ご】数える count five (aloud / with a finger)
- 五【いつ】つ数える count five (aloud / with a finger)
- ボールの数を数える count the number of balls
- ボールを数える count the balls
You can omit を in the last two examples in casual conversations.
"十数えました" or "十数える" is correct. Japanese native speakers feel comfortable using this expression, so it is probably idiomatic.
"十を数えました" or "十を数える" is correct and almost natural. (Some Japanese native speakers might feel these expressions are unnatural.)
If you count "人数" or "車の台数", you have to use を resulting in: "人数を数えました" or "人数を数える", "車の台数を数えました" or "車の台数を数える."
For native speakers of Japanese, the expressions "人数数えました", "人数数える", "車の台数数える" and "車の台数数えました" would be unnatural, and we would need the を.