In Japanese, the words "間" (あいだ, aida) and "間に" (あいだに, aida ni) are used to express the concept of "while" or "during." However, they have slightly different nuances and uses.

1. 間 (あいだ, aida)

"間" refers to the duration or the entire span of time during which an action or state occurs. When you use "間," it implies that the two actions or states are happening simultaneously over a continuous period.

Structure:

• Verb (て-form) + いる + 間

  This structure is used when the first action or state is continuous, and the second action occurs throughout that period.

  Example:

  • 彼が宿題をしていた間、私はテレビを見ていた。 (Kare ga shukudai o shite iru aida, watashi wa terebi o mite ita.) "While he was doing his homework, I was watching TV."

• Noun + の + 間

  This structure is used with nouns to express that something happens during the entire duration of a certain period.

  Example:

  • 夏休みの間、毎日泳いでいた。 (Natsuyasumi no aida, mainichi oyoide ita.) "During the summer vacation, I swam every day."

2. 間に (あいだに, aida ni)

"間に" emphasizes that the second action occurs at some point within the duration of the first action or state. It’s often used when the second action happens as a one-time event rather than something continuous.

Structure:

• Verb (て-form) + いる + 間に

  Use this structure when you want to indicate that a specific event happens at some point during the continuous action.

  Example:

  • 彼が宿題をしている間に、私は洗濯をした。 (Kare ga shukudai o shite iru aida ni, watashi wa sentaku o shita.) "While he was doing his homework, I did the laundry."

• Noun + の + 間に

  Similar to the above, but used with nouns. It indicates that the action happens at some point during the specified time period.

  Example:

  • 夏休みの間に、旅行に行った。 (Natsuyasumi no aida ni, ryokou ni itta.) "During the summer vacation, I went on a trip."

Summary:

• 間 (aida): "While" or "during," implying that two actions/states are occurring simultaneously over a period.
• 間に (aida ni): "While" or "during," but emphasizes that the second action happens at a specific point within the duration of the first action.

Knowing the distinction between "間" and "間に" helps in choosing the right expression depending on whether the action is continuous or happens at a specific point in time.

Difference vs ながら

Here's a quick summary of the differences:

• ながら: Indicates two simultaneous actions performed by the same subject.
  • Example: 歩きながら話す ("Talk while walking").
• 間: Describes two actions happening continuously over the same period, possibly by different subjects.
  • Example: 私が勉強している間、彼女はテレビを見ていた ("While I was studying, she was watching TV").