当初

1. Origins, structure, and basic meaning

• Structure: 当初 (とうしょ) is a temporal noun and adverb for the initial stage when something began.
• Basic usage: 当初の予定より早い modifies the original schedule, while 計画は当初、三人で始める adverbially states the plan at its initial stage.

2. Common pitfalls and similar expressions

• Original schedule and initial intention
  • 当初の予定 is a noun phrase serving as the comparison baseline, whereas 当初、 supplies temporal background for the sentence. Neither guarantees the plan remains unchanged now.