但し

1. Origins, structure, and basic meaning

• Structure: 但し is read as ただし and adds a condition, exception, or qualification to what precedes it.
• Basic usage: It can introduce exceptions to permission or a registration requirement attached to optional participation.

2. Common pitfalls and similar expressions

• Adding an exception
  • 但し: It qualifies the permission to copy by excluding some materials. Example: 図書館の資料はコピーできる。但し、一部を除く。
• Adding a requirement
  • 但し: It adds advance registration as a requirement for participation. Example: 参加は自由です。但し、事前の申込みが必要です。