What is the difference between 間 and 間に？

1. 間 (あいだ)

• Meaning: To do something and something takes place for the entire duration of an action or state.
• Usage: Used when the action or state lasts for the entire period.
• Example:
  • 私は昼ごはんの間、友達と話しました。
    I talked with my friend (the whole time) during lunch.
  • 子どもが寝ている間、私はテレビを見ていた。
    I was watching TV (the whole time) while my child was sleeping.
  • 友だちを待っている間、宿題をしていた。
    I was doing my homework (the whole time) while waiting for my friend.
• For a better understanding of this grammar 間（あいだ）、go to 間（あいだ）grammar format.

2. 間に (あいだに)

• Meaning: Refers to something that happens at some point during the duration of another action or state.
• Usage: Used when the action occurs at some point within the period, not necessarily for the entire duration.
• Example:
  • 昼ごはんの間に、友達が来ました。
    My friend came during lunch.→In this case, “間に” indicates that the friend came at some point during lunch, but not necessarily for the entire lunch.
  • 子どもが寝ている間に、地震がありました。
    There was an earthquake while my child was sleeping.
  • 夏休みの間に、たくさん旅行したい。
    I would like to travel a lot during summer vacation. → It doesn’t necessarily mean to travel for the entire summer vacation.
• For a better understanding of this grammar 間（あいだ）、go to 間に（あいだに）grammar format.
  

Summary:

• 間 (あいだ): Emphasizes the entire period of an action or state.
• 間に (あいだに): Focuses on an event occurring within the period of another action or state.