有効

1. Origins, structure, and basic meaning

• Structure: 有効 is a noun and na-adjective read ゆうこう, meaning either valid within a period or effective for a purpose.
• Basic usage: Use まで有効 for a validity limit and 話し合いには…有効だ for a method effective in discussion.
  • この券は今月末まで有効です。 says that the pass is valid through the end of the month; 話し合いには時間を区切る方法が有効だった。 says that dividing the time was effective for the discussion.

2. Common pitfalls and similar expressions

• まで有効
  • まで marks the final point through which validity continues.
• 話し合いには有効
  • には limits the area in which the method is effective to the discussion.
• The two senses of 有効
  • With a pass or qualification it means valid; with a method or measure it means effective.