Meaning & Usage
✨ Basic Meaning
To decide to do something; to make a resolution.
🎯 Primary Function
Expresses the speaker’s personal decision or resolution to do something, often made at that specific time or recently.
📋 Grammar Structure
Verb (Dictionary Form) + ことにする
🎭 Usage Contexts
Formal Situations
Can be used, but more formal expressions like Verb Dictionary Form + ことといたします might be preferred in very polite contexts.
Informal Situations
Very common and natural.
Written Language
Frequently used in informal writing (diaries, personal emails) and sometimes in more formal contexts to express a company’s or group’s decision (e.g., 会議の結果、A案にすることにした – “As a result of the meeting, we decided on Plan A”).
Spoken Language
Extremely common in everyday conversation.
💡 Common Applications
Expressing a personal resolution about a future action.
This is the most common use, indicating a decision the speaker has made.
Example: 明日からジョギングをすることにします。 (Ashita kara jogging o suru koto ni shimasu.) – “I’ve decided to start jogging from tomorrow.”
Reporting a decision made by a group or oneself.
Can be used to state a decision that has been finalized.
Example: 来週、旅行に行くことにしました。 (Raishuu, ryokou ni iku koto ni shimashita.) – “We decided to go on a trip next week.”
Stating a general rule or agreement (less common for N4).
Sometimes used to express a general principle or agreement that one has personally adopted or that a group has made (often in the past tense).
Example: 毎日、漢字を５つ覚えることにしています。 (Mainichi, kanji o itsutsu oboeru koto ni shite imasu.) – “I make it a rule to memorize 5 kanji everyday.” (This is ことにしている, related but different).
Frequency
Very frequent in daily conversation when talking about plans and decisions.
Difficulty
Relatively easy for N4, primarily focused on understanding the “personal decision” nuance vs. “rule” (~ことになっている).
Example Sentences
もうすぐ夏休みなので、国へ帰ることにしました。
Summer vacation is coming soon, so I decided to go back to my home country.
お金がないから、今日は外食しないことにする。
Because I have no money, I’ve decided not to eat out today.
健康のために、甘いものを食べるのをやめることにします。
For the sake of my health, I’ve decided to stop eating sweets.
Notes & Nuances
📌 Important Points
Expresses a personal decision
The key nuance is that the decision is made by the subject of the sentence (usually the speaker).
Example: 私は毎日日本語を勉強することにします。 (Watashi wa mainichi Nihongo o benkyou suru koto ni shimasu.) – “I’ve decided to study Japanese every day.” (My own decision).
Often implies a resolution
It’s not just a temporary thought, but a commitment or resolution.
Example: タバコをやめることにしました。 (Tabako o yameru koto ni shimashita.) – “I decided to quit smoking.” (A strong resolution).
⚠️ Common Mistakes
❌ Confusing with ~ことになっている (~koto ni natte iru)
✅ ことにする = speaker’s decision; ことになっている = rule/agreement/plan decided by someone/something else or by circumstance.
Using ことにする when talking about a public rule (e.g., 病院ではタバコを吸わないことにする – incorrect) instead of ことになっている (病院ではタバコを吸わないことになっています – correct).
❌ Confusing with ~ことにしている (~koto ni shite iru)
✅ ことにする = decision made at a point in time; ことにしている = a habit or rule one has decided for oneself and continues to follow.
Using ことにする when describing a long-standing habit (e.g., 毎日早く寝ることにする – might sound like a one-time decision) instead of ことにしている (毎日早く寝ることにしています – means “I make it a rule to go to bed early every day”).
🏛️ Cultural Context
Politeness Level: Standard politeness when using します form. casual with する form.
Social Situations: Used widely in both personal and professional contexts to state decisions.
Regional Variations: No significant regional variations in meaning or usage.
🔍 Subtle Differences
ことにする vs. ことになっている
にする expresses a decision made by the subject; になっている expresses a state of affairs, a rule, or a plan that has been decided by others or circumstance.
When to use: Use にする when you are the one making the decision. Use になっている when describing a rule, schedule, or something decided externally.
ことにする vs. ことにしている
にする is a decision made now or at a specific past time; にしている is a decision made in the past that has become a standing habit or rule for oneself.
When to use: Use にする for a one-off or recent decision. Use にしている for a continuous practice based on a past decision.
ことにする vs. ～たい (~tai) / ～つもりだ (~tsumori da)
～たい expresses desire; ～つもりだ expresses intention or plan; ～ことにする expresses a firm decision/resolution.
When to use: Use ～たい for what you want to do. Use ～つもりだ for a plan you have. Use ～ことにする when you have made a definite decision.
📝 Conjugation Notes
Verb (Dictionary Form) + ことにする/ことになりました/ことにしました/ことにしている
🔊 Pronunciation Tips
The pitch slightly rises on “こと” and falls on “する”. Pronounce “ni” clearly.
🧠 Memory Tips
Think of こと (koto) as “the matter of” or “the action of”, and にする (ni suru) as “to decide upon”. So, “to decide upon the matter of doing X”.
Practice Exercises
毎日、____ (read a book) ことにしました。
本を読む
本を読んだ
本を読んで
本を読むの
健康のために、肉を食べるのを____ ことにします。
やめる
やめない
やめた
やめたい
I’m a software engineer based in Japan, with experience in developing web and mobile applications. I’m passionate about technology, especially in DevOps, AI, and app development using platforms like AWS, Flutter, and Node.js. My goal is to build a website that shares knowledge about the Japanese language and IT, helping everyone learn and grow more easily in the digital era.
