How to say "chiefly" in Japanese

• 主としてしゅとしてCommon
  expression, adverbCovers 'chiefly' as 'primarily' or 'for the most part'. It largely overlaps with 主に, and in most sentences either word will do; it simply frames the element in question as the primary one.
  これらの手紙てがみは主ぬしとして母ははから来きたものだ。↗

  These letters, in the main, are from my mother.
• 主におもにJLPT N3approx.Common
  adverbThe plain, all-purpose adverb for 'chiefly' meaning 'mainly' or 'mostly'. When you simply need to point to the main part of something, this is the word to reach for.
  彼かれの病気びょうきは主おもに精神的せいしんてきな物ものだった。↗

  His illness was mainly psychological.
• もっぱらJLPT N1approx.Common
  adverb, no-adjectiveSuits 'chiefly' when the idea shades toward 'exclusively' — one pursuit occupying someone to the near-exclusion of everything else. For a neutral 'mainly' it can feel too strong. Usually written in kana alone.

All three translate 'chiefly' as 'mainly': use 「主に」 for the neutral everyday sense, 「主として」 as the near-synonymous option that also covers 'for the most part', and 「もっぱら」 when the meaning borders on 'exclusively'.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 主としてしゅとしてmainly
• 主におもにmainly
• 多くおおくmostly
• もっぱらprincipally