せい（せい、sei）
- because of

The Japanese word せい has several meanings and usages. It often indicates a "reason," "cause," or "due to." It can also express "because of" or "owing to." Furthermore, せい can be used to indicate a negative result or consequence, often implying blame or responsibility. It is crucial to understand the context to interpret せい correctly. Finally, せい can sometimes be used to mean "nature" or "character," though this is less common.

⚫︎雨のせいで、試合は中止になった。 Translation: The game was cancelled because of the rain. ⚫︎彼のせいで、計画が台無しになった。 Translation: The plan was ruined because of him. ⚫︎食べ過ぎのせいでお腹が痛い。 Translation: My stomach hurts because I ate too much.

せい is frequently used at the end of a clause or sentence to indicate the reason or cause of something. It often follows a noun (connected by の), or a verb/adjective in its plain form. Be mindful of the negative connotations it often carries, implying that the reason is either undesirable or a negative outcome.

せい is primarily written in hiragana. The kanji version is 為, but it's less commonly used in modern Japanese. There are no variations in the okurigana, as it is just written as せい.

⚫︎ ため (tame) - similar meaning of "because of" or "for the sake of", but less often carries the implication of blame. ⚫︎ から (kara) - "because" or "since," a more general term for reason. ⚫︎ おかげ (okage) - "thanks to," implies a positive result or consequence. ⚫︎ ゆえに (yueni) - "because of," a more formal equivalent.

⚫︎ It doesn't have a direct antonym. However, to express the opposite, you would rephrase the sentence to remove the implication of blame or the negative outcome. You can switch to use words such as おかげ (okage) if the situation gives positive results.

寝不足のせいで、今日は集中できない。 ・Translation: I can't concentrate today because I didn't get enough sleep. ・Explanation: This sentence uses せい to explain that the reason for not being able to concentrate is the lack of sleep (寝不足). It implies a negative consequence.

彼の怠惰のせいで、プロジェクトは遅れている。 ・Translation: The project is behind schedule because of his laziness. ・Explanation: This sentence clearly shows the negative connotation of せい, blaming "his laziness" for the delay of the project.

The origin of せい is rooted in the concept of "doing" or "action." It evolved to express the causal relationship between an action or event and its consequence. The kanji 為 literally means "to do," "to make," or "to cause," further illustrating its connection to the notion of cause and effect.