Japatan
Formation
- V辞書形 + ことだ
- Vない形 + ないことだ
Explanation
Used to give advice: "the best thing to do is ~" or "it is important to ~." It sounds firm and personal, so it is usually said by someone in a higher position, such as a teacher to a student or a senior to a junior. 〜ないことだ means "you should not ~." In conversation you often hear 〜ことだね or 〜ことですよ.
Examples
日本語が上手になりたければ、毎日少しでも話すことだ。
If you want to get good at Japanese, you should speak it every day, even just a little.
試験の前の日は、あまり遅くまで起きていないことだ。
The day before an exam, you shouldn't stay up too late.
分からないことがあったら、一人で悩まないで、先輩に聞くことですよ。
If there's something you don't understand, don't worry about it alone. Ask a senior colleague.
旅行の前に、ホテルの場所をよく調べておくことだね。
Before you travel, it's best to check carefully where your hotel is.
Notes
It can sound rude toward someone above you, so with teachers or bosses use 〜たほうがいいと思います instead. 〜べきだ states a general rule or what is right; 〜ことだ is advice to the person in front of you.
Related grammar
Mini quiz
1やせたいなら、甘いものを食べすぎない（ ）。
Answer and explanation
Answer: 2 ことだ
"If you want to lose weight, you shouldn't eat too many sweets." 〜ないことだ gives advice. The other choices do not express advice.
2試合に勝ちたければ、毎日（ ）ことだ。
Answer and explanation
Answer: 1 練習する
"If you want to win games, you should practice every day." Advice ことだ follows the dictionary form of a verb, not the te-form, ta-form, or volitional form.
3A「最近、よく眠れないんです。」
B「寝る前にスマホを（ ）ことだよ。」
Answer and explanation
Answer: 3 見ない
"I can't sleep well lately." "You shouldn't look at your phone before bed." Use the nai-form (〜ない) + ことだ. The other forms do not connect to ことだ.
