入る

1. Origins, structure, and basic meaning

• Structure: 入る is a godan intransitive verb read はいる, meaning to enter or to fit within a space. Its past form is 入った.
• Basic usage: It can describe going inside a store or state the number of plates a box can hold.
  • 雨が強くなったので店の中に入った。 says that the speaker went inside the store because the rain intensified; この箱には大きな皿が五枚入る。 says that five large plates fit in this box.

2. Common pitfalls and similar expressions

• 中に入る
  • に marks the inside of the store as the destination entered.
• 皿が五枚入る
  • が marks the item that fits, and 五枚 counts the five flat plates.
• 入る and 入れる
  • 入る is intransitive and describes entering or fitting, while 入れる is transitive and means putting something inside.