Japanese keigo (honorifics) splits into three forms: teineigo (polite), sonkeigo (respectful), and kenjogo (humble). Picking the wrong one — even with otherwise perfect grammar — makes business writing sound rude, cold, or strangely formal. This post explains the three forms and when to use each in business email, internal documents, and external communication.
The three forms of keigo
1. Teineigo (polite form)
The default "polite register". Ends sentences with desu, masu, or gozaimasu. Safe for almost everyone — colleagues, casual business contacts, customers in low-pressure contexts. AI translators default here.
2. Sonkeigo (respectful form)
Used when the subject is the other party — the boss, the customer, the senior. miru (to see) becomes goran ni naru, iu (to say) becomes ossharu. You're elevating their action.
3. Kenjogo (humble form)
Used when you are the subject and you want to lower your own action to indirectly raise the listener. miru becomes haiken suru, iku (to go) becomes ukagau.
Which form to use, by situation
Internal email to a peer: teineigo only. Adding sonkeigo or kenjogo feels distant.
Internal email to a senior or executive: teineigo + targeted kenjogo for your own actions ("資料をお送りいたしました") and targeted sonkeigo for theirs ("部長がおっしゃった件について").
External email to a client: the full combo — teineigo + sonkeigo + kenjogo plus cushion phrases like "お忙しいところ恐縮ですが…"
Contract or formal document: teineigo + kenjogo; no sonkeigo.
Getting AI translation to pick the right register
Off-the-shelf translators (Google, DeepL) guess the register from sparse context. Giving the AI three pieces of information radically improves output:
- The recipient's relationship (peer, manager, client, first contact)
- The document type (email, contract, internal memo, proposal)
- The relationship history (long-term client vs cold outreach)
BizHonyaku surfaces these as a dropdown — pick "External email to a new client" and the same English sentence comes out heavier on kenjogo and cushion phrases than if you picked "Internal Slack-like message". The grammar is the easy part; the register is the work.