に

1. Origins, structure, and basic meaning

• Structure: Add に to the stem of a na-adjective to modify the following action.
  • 静かだ → 静かに, きれいだ → きれいに
• Basic usage: It describes how an action is performed or the state produced by that action.
  • 静かに片づける focuses on tidying quietly, while きれいに片づける focuses on leaving things clean and tidy.

2. Common pitfalls and similar expressions

• Where な and に belong
  • Use 静かな部屋 to modify a noun and 静かに話す to modify an action. Do not follow な with に.
• Distinguishing i-adjectives
  • An i-adjective normally changes its final い to く, as in 早い → 早く.
  • Although きれい ends in the character い, it is a na-adjective and becomes きれいに.