いずれにせよ

いずれにせよ is a formal conjunction-like adverb used to introduce a conclusion that holds true regardless of the preceding circumstances. It typically appears at the beginning of a sentence.

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This is a written/formal expression, common in essays, news, speeches, and business communication. It sounds stiff in casual conversation.

Forms

• いずれにせよ: most formal
• いずれにしても: formal, slightly softer
• どちらにせよ: formal, implies choosing between two stated options
• どちらにしても: somewhat formal, between two options

いずれ〜 forms cover any number of possibilities, while どちら〜 forms assume exactly two. せよ (the classical imperative of する) is stiffer than しても in every pair.

Casual equivalents

• とにかく: anyway (general-purpose, casual)
• ともかく: anyhow (casual, slightly literary)
• どっちにしても: either way (casual spoken form)

Common patterns

Followed by a statement of conclusion or decision — often an obligation (なければならない) or a prediction. It typically follows a clause that raises alternatives or admits uncertainty: 〜か〜か分(わ)からないが、いずれにせよ…