Politeness levels

Japanese politeness is a foundational concept called honorifics（敬語）. It acts as a 'social lubricant' to define relationships based on the in-group vs. out-group（内・外）dynamic. In this system, you must humble your own 'in-group' (like your family or boss) when speaking to an 'out-group' person (like a client).

The modern standard, officially established by the 2007 Cultural Affairs Agency 'Guidelines for Honorifics'（敬語の指針）, recognizes five categories. Older or simplified textbooks often use a three-category system, grouping Humble I and II together as 'Humble language'（謙譲語）, and grouping Polite language and Word beautification together as 'Polite language'（丁寧語）:

• Polite language（丁寧語）: Standard polite language using the ます form, です, and でございます (or ございます). This is the 'safe' level for strangers or colleagues.
• Respectful language（尊敬語）: Respectful language used to elevate the other person's actions, state, belongings, or existence (e.g., お忙しい, ご家族). Common patterns include お/ご〜になる and the passive form. It also relies on essential irregular verbs like いらっしゃる and 召し上がる. You never use this for yourself.
• Humble language I（謙譲語I）: Humble language used when your action is directed at a specific person you want to elevate. It shows respect to the receiver of the action. Common patterns include お/ご〜する and 〜させていただく (to humbly receive permission to do something). It also relies on specific irregular verbs like 伺う and 申し上げる. You never use this for the listener's or an out-group's actions.
• Courteous language / Humble language II（丁重語）: Courteous language used for the speaker's (or in-group's) own actions to show respect to the listener of the conversation, regardless of who the action is directed at. It relies heavily on specific irregular verbs (e.g., 参る, いたす). You never use this for the listener's or an out-group's actions. Furthermore, these verbs are rarely used in their plain dictionary form at the end of a sentence and are almost exclusively followed by Polite language (ます) (e.g., 参る becomes 参ります, いたす becomes いたします).
• Word beautification（美化語）: 'Beautification' of words to make one's speech sound more refined. Unlike the other four categories, it does not show respect to anyone, but simply makes the speaker's own language sound elegant. This involves adding the prefixes 'お' or 'ご' to nouns, as well as using elegant word substitutions (such as saying おなか instead of 腹, or おいしい instead of うまい). As a general rule for prefixes, 'お' is used with native Japanese words（和語）like お金 or お水, while 'ご' is used with Sino-Japanese words（漢語）like ご飯 (though there are exceptions like お茶). Additionally, 'お' and 'ご' generally cannot be attached to Western loanwords (katakana words). This is why native speakers prefer using elegant vocabulary like お手洗い instead of adding 'お' to トイレ (おトイレ is generally considered incorrect). Note that the exact same お/ご prefixes are used across Respectful, Humble I, and Word beautification. The politeness category simply changes based on whose noun or action it is attached to (e.g., your family = Respectful; my explanation to you = Humble I; the tea = Beautification).

Becoming proficient in these levels is essential because using the wrong level can make you sound either rude or strangely arrogant.