～せい

About

せい is a dependent noun that is used to indicate blame, or that "X" negative outcome is a result of "Y". ～せい attaches to the casual form of verbs and い-adjectives, to nouns using の, and to な-adjectives using な.

～せい is often followed by the で particle.

E.g. 砂糖さとうを入いれるのを忘わすれたせいで、マフィンが美味おいしくなかった。"The muffins weren't good because I forgot to add sugar."

せい can be followed by か when the reason for a given outcome is uncertain. ～せいか can be used in both negative and positive contexts.

E.g. ストレスのせいか、食欲しょくよくが止とまらない。 "I'm not sure if it's due to stress, but I can't stop eating."

The ～せいにする pattern can be used to assign blame to someone/something.

E.g. 失敗しっぱいを、全部ぜんぶ人ひとのせいにするのはよくありません。 "It's not good to blame all of your mistakes on others."

Summary

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  ～せい is used to indicate blame

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  ～せいか can be used when we are unsure of the cause of something

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  ～せいか can be used in positive and negative contexts

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  ～せいにする can be used to assign blame