"unfinished" sentences ending in particles like を, に and が

Question

This is something I've always wondered about, but can't find any info about.

When native speakers come across a sentence that ends ...を。, ...と。 or ...が！*, how do their brains parse it? Is it just a case of being able to guess what word would follow based on their past exposure to collocations (words that go together with other words) and situations?

I found this question to which the answers say it's verb ellipsis, which I get, but I'd like to know if there's any way of knowing exactly which verb – if there is indeed only one particular possibility — or whether the hidden verb belongs to a small group of verbs which are often omitted. For example, on TV an announcer said something like 次の日はすごい状態に！ I asked a Japanese friend what the verb would be and they immediately said なった. Is it likely they knew this from collocational knowledge, the same way an English speaker could finish the sentence running around like a chicken with...? And could なった have just as easily been a different verb it was a different situation, or is 状態に always followed by なる if the verb is dropped?

*(not the が that means "but"; the other one. I have no idea how to interpret sentences that end with が – it's the most difficult one for me.)

More examples: Here and here

Answer 1

In my experience, there is usually some other context that was previously given, or is completely obvious even though it's omitted. I refer to the former as a kind of "back reference" to whatever was said before.

• A: めっちゃ難しい...　→　It's so hard/difficult
• B: 何が？　→　What is? (Since you would say Ｘが難しい)
  
  or
• A: 明日母に送るわ。　→　I'll send it/this to my mother tomorrow. (Perhaps person B is out of the room and cannot see what A is talking about)
• B: 何を？　→　What (will you send)? (Since you say Ｘを送る)

or

• ルールに書いてあります。キーパー以外の選手がボールに手を触れないようにと　→　It's written in the rules. "No player besides the goalie shall touch the ball with their hands".　→　Here, the と is the quotation marker, making the entire second sentence the "it" that's referenced in the first.

Some examples I often see of the implied-yet-omitted context are like

• 良い一日を！　→　Have a good day　→　The "have" is omitted, but could/would be something like 過ごしてください

ように is very common to see at the end of a sentence to indicate "May something happen" / "Let it be that 〜"

• 今年も祝福いっぱいの一年になりますように　→　(Said to someone on their birthday) "May this year (also) be one full of blessings"　→　The omission is clearly something like "I hope" (願っています) or "I pray" (祈っています)

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For the book in your first example link, it's titled 夢に日付を！. It even says in English at the bottom "Date Your Dream", which, while grammatically correct, would be better translated as "Set a date for your dream (to come true)". In this case, the "Set" part is what is omitted, so the full Japanese could be something like 夢に日付を入れる. I can't really explain how, but leaving off the 入れる gives is more of an impact as a book title.