ことに

Attached to a word expressing emotion or evaluation, it introduces a fact by first stating how the speaker feels about it: "to my surprise…", "unfortunately…", "what is ~ is that…".

Somewhat written in tone, it is common in essays, news, speeches and careful narration. It is placed before the main clause, usually at the start of the sentence or right after the topic (彼は、驚いたことに、…), and uses emotion words such as 驚いた, 残念な, 嬉しい, 悲しい and 困った. Unlike sentence-final exclamatory patterns, it sets up an emotional frame, and the main clause is a plain report of fact.

• ことかN3ことか is used at the end of the sentence, often echoing words like どんなに, どれほど, or 何度, to exclaim how deep something is or how many times it has happened; ことに states the feeling first at the start of the sentence, followed by a statement. The two cannot be swapped.
• 限りだN1限りだ is placed at the end of the sentence to express emotion, meaning 'extremely...'; ことに sets up the feeling first, and the following clause is a statement of fact or conjecture. 限りだ can attach to a noun + の but not to verbs, while ことに can attach to the ta-form of a verb, so they cannot be used interchangeably.
• ことになるN4ことに attaches to words expressing feelings or evaluations, usually placed at the start of the sentence to point out the speaker's feeling, and is rather literary; ことになる attaches to verbs and expresses an arrangement, result, or calculated conclusion in a neutral register. They look similar but differ in meaning and cannot be swapped.
• ことだN3ことだ comes at the end of the sentence, attaching to the dictionary form or ない-form of a verb, to give advice meaning 'you had better...'; ことに attaches to a feeling word placed earlier and expresses the speaker's feeling, with the following clause being merely a statement, not a suggestion. The two cannot be swapped.
• ものだN2ものだ comes at the end of the sentence to exclaim about general truths or changes in someone or something, and can also express nostalgic recollection or advice based on common sense; ことに is placed at the start of the sentence, presenting the feeling first and then making a statement, with a more literary flavor. The two cannot be swapped.

ことに comes before the main clause, at the head of the sentence or after a topic (彼は、驚いたことに、…), and colors the fact that follows, whereas ことか, 限りだ, and the exclamatory uses of ことだ and ものだ come at the end of a sentence to express the feeling itself. ことになる is unrelated in meaning: it describes an arrangement or outcome ("it has been decided that…").