This means that no matter which choice you make, the result will be the same. It's like saying 'whether A or B, it's the same'.
Noun + にせよ + Noun + にせよPrimary
Verb [dictionary form] + にせよ + Verb [dictionary form] + にせよ
い-Adjective + にせよ + い-Adjective + にせよ
な-Adjective + にせよ + な-Adjective + にせよ
This means that no matter which choice you make, the result will be the same. It's like saying 'whether A or B, it's the same'.
行くにせよ行かないにせよ、早めに決めて連絡してください。
Whether you go or not, please decide and contact us early.
国内旅行にせよ海外旅行にせよ、準備を怠ってはいけない。
Whether it's domestic travel or international travel, you must not neglect preparations.
賛成にせよ反対にせよ、会議で自分の意見をはっきり述べなかったのは問題だ。
Whether you agreed or disagreed, it's a problem that you didn't clearly state your opinion in the meeting.
新品にせよ中古品にせよ、このモデルはもう手に入らないだろう。
Whether new or used, this model is probably no longer available.
成功にせよ失敗にせよ、この経験は彼の将来にとって大きな財産となった。
Be it success or failure, this experience became a great asset for his future.
Think of it like choosing between two roads. No matter which road you take, you still end up at the same place. The two things you mention don't change the main idea.
This is like "〜にしろ〜にしろ". But "〜にせよ〜にせよ" is more formal. You use it in writing. This includes essays or reports. You also use it in formal speeches. "〜にしろ〜にしろ" is more common. You can use it in many situations. This includes formal talks and casual chats. "〜であれ〜であれ" is also very formal. It is often used with nouns.
Don't use this when you talk about what you want. For example, you can't say, "Whether it's sunny or rainy, I want to have fun." The main part of the sentence must be a fact. It can be a judgment or a rule. It must be something that is true no matter what. It should not be your own wish or hope. It should not be what you plan to do.
More formal alternatives(1)
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