経つ

1. Origins, structure, and basic meaning

• Structure: 経つ is read as たつ and is an intransitive verb for time or a period elapsing.
• Basic usage: Elapsed duration appears in 三年が経つ, while progressive change appears in 時間が経つほど.

2. Common pitfalls and similar expressions

• Spelling versus 立つ
  • The homophone 立つ means to stand; elapsed time is written 経つ.
• Time as subject
  • The period itself takes が in 時間・年月が経つ, rather than being a direct object acted upon.