by means of

1. Origins, structure, and basic meaning

• Structure: 以 forms compounds relating to a reference point or range and is read い.
• Basic usage: 以上, read いじょう, means at or above a threshold; 以下, read いか, means at or below it; 以外, read いがい, means outside or other than.

2. Common pitfalls and similar expressions

• Including the threshold
  • In quantities, 三つ以上 includes three and more, while 三つ以下 includes three and fewer.
  • Translating these as strictly more or fewer than three changes the range.
• Excluding a category
  • 日曜日以外 means everything relevant except Sunday.
  • It separates what is included, rather than comparing larger and smaller quantities.
• A previous time
  • 以前, read いぜん, means “formerly” when used on its own.
  • 以前ここに住んでいた means having lived here before, without specifying a particular year.