決める

1. Origins, structure, and basic meaning

• Structure: 決める, read きめる, means settling something through choice or discussion.
• Basic usage: Use it for deciding matters such as a travel schedule or a meal.

2. Common pitfalls and similar expressions

• Deciding and being settled
  • 決める describes someone deciding something, while 決まる describes something becoming settled.
• What is decided
  • In the example 日程を決める, を marks what is decided.
• An already-decided state
  • The example's 決めていた describes an already-decided state at the relevant past time.