当時

1. Origins, structure, and basic meaning

• Structure: 当時 (とうじ) is a noun and adverbial expression meaning at the particular time of an event under discussion.
• Basic usage: It modifies a noun in 当時の写真 or sets the time frame adverbially in 私は当時.
  • 当時の写真を見ると町の変化が分かる。 — Photographs from the time show how the village has changed.
  • 私は当時まだ学生で、その店によく通った。 — I was still a student then and often visited that store.

2. Common pitfalls and similar expressions

• Reference time
  • 当時 points to a past time already established by context. Unlike 昔, the general past or old days, it needs a specific reference period.