How to Use “～せいで / ～せいだ” in Japanese: Expressing Blame and Negative Causes

Introduction

In Japanese, you already learned how to say “thanks to…” for a positive result using ～おかげで (okage de). But what happens when things go wrong and you want to say “because of…” or point the finger of blame?

When a specific cause or reason leads to a negative or undesirable result, we use the exact opposite grammar point:

～せいで = because of (something bad)… / due to the fault of…

Let’s learn how to use this grammar structure to correctly express negative causes—and learn the important social rules to avoid hurting someone’s feelings!

1. Meaning: What does ～せいで mean?

～せいで (sei de) clearly indicates that a preceding noun, verb, or adjective is the direct cause of a bad situation.

If you say that an event or object is the cause (e.g., 雨あめのせいで / because of the rain), you are expressing your dissatisfaction with the situation. If you use it with a person, you are explicitly placing the blame on them.

2. Formation

This grammar point attaches to the plain form (普通形) of verbs and adjectives. Pay close attention to nouns and な-adjectives, which require an extra particle.

*Note: If you want to use this grammar point at the very end of a sentence, it changes to ～せいだ (casual) or ～せいです (polite).

3. Sentence Patterns and Examples

Pattern A: [Cause] せいで [Negative Result]

This is the standard way to say “Because of X, bad thing Y happened.”

彼かれが遅刻ちこくしたせいで、映画えいがに間まに合あいませんでした。
Because he was late, we didn’t make it to the movie.

全然運動ぜんぜんうんどうしなかったせいで、病気びょうきになってしまった。
Because I didn’t exercise at all, I got sick.

最近さいきん、仕事しごとが忙いそがしいせいで、あまりゲームができていない。
Lately, I haven’t been able to play many games because I’ve been so busy with work.

Pattern B: [Result] のは [Cause] せいだ / せいです

If you want to state the negative result first and then explain why it happened, you can use 〜のは、〜せいです (The reason [Result] happened is because of [Cause]).

太ふとったのは、毎日まいにちお菓子かしを食たべているせいです。
The reason you gained weight is because you eat sweets every day.

赤あかちゃんがいつも泣なくのは、私わたしの顔かおが怖こわいせいだ。
The reason the baby always cries is because my face is scary.

日本にほんが少子高齢化しょうしこうれいかなのは、教育費きょういくひが高たかいせいだと思おもいます。
I think the reason Japan has a low birth rate and an aging population is because of the high cost of education.

4. Important Warning!

When using 「＜人＞のせいで」 (Because of [Person]), it clearly communicates that “the bad result is that person’s fault.”

If you say this directly to someone (e.g., あなたのせいで – Because of you), it can easily make them feel bad or sound incredibly accusatory. Please be very careful and generally avoid saying this directly to someone unless you actually intend to blame them for a mistake!

5. Related Grammar

～おかげで・～おかげだ (Thanks to…)

While ～せいで is used for negative outcomes and pointing blame, ～おかげで is its exact opposite. You use it when a specific cause leads to a positive or desirable result, expressing gratitude.

• ✅ 先生せんせいのおかげで、テストに合格ごうかくできました。(Thanks to my teacher, I was able to pass the test.)
• ❌ 先生のせいで、テストに合格できました。(Because of my teacher, I was able to pass the test. ➔ Wait, are you mad at the teacher for helping you pass?!)

You can learn all about how to use this positive grammar point in our dedicated guide to ～おかげで!

Bonus Phrase: 気のせい (Ki no sei)

One of the most common phrases you will hear in Japanese using the word sei is 気のせい (ki no sei). It literally means “because of my mind/spirit,” but it translates to “just my imagination” or “in my head.”

• A: 今いま、誰だれか泣ないていなかった？ (Was someone just crying?)
• B: 気きのせいじゃない？ (Isn’t it just your imagination?)

If you think you saw or heard something strange but aren’t sure, you can just say: 気のせいか。(Must be my imagination.)

6. Practice

Choose the correct word for each sentence. Is it a positive result (おかげで) or a negative result (せいで)?

1. 薬くすりを飲のんだ [ おかげで / せいで ]、熱ねつが下さがりました。
   Because I took medicine, my fever went down.
2. 電車でんしゃが遅おくれた [ おかげで / せいで ]、会議かいぎに遅刻ちこくしました。
   Because the train was late, I was late for the meeting.
3. スマホを忘わすれた [ おかげで / せいで ]、何なにもできません。
   Because I forgot my smartphone, I can’t do anything.

Answers:

1. おかげで (Positive result)
2. せいで (Negative result)
3. せいで (Negative result)

FAQ

Conclusion

Mastering ～せいで (sei de) is a great way to talk about the causes behind unfortunate events or mistakes.

• Use Noun + のせいで for things or people.
• Use Verb / i-adjective (Plain form) + せいで for actions or states.
• Use na-adjective + なせいで for describing conditions.
• Remember to use it only for negative outcomes, and be polite when talking about other people!