開始 and 再開: starting an activity and resuming it
Compare opening a process with resuming interrupted work, keeping the restart time separate from final completion.
Beginning work or an activity
開始, read かいし, means starting work or an activity. 受付は午後一時に開始します。 says that registration begins at one in the afternoon.
開始前に道具をそろえてください。 asks someone to prepare the tools before the start. Preparation precedes the beginning.
Continuing an interrupted activity
再開, read さいかい, means resuming an interrupted activity. 雨で中断した作業を再開しました。 says that work interrupted by rain was resumed.
工事は来月再開する予定です。 says that construction is scheduled to resume next month. It does not report a restart that has already happened.
A new activity and an activity continued
新しい講座を開始します。 announces the start of a new course. 中断していた講座を再開します。 announces the resumption of a course that had been interrupted.
作業は再開しましたが、完成はまだ先です。 says that work has resumed but completion is still some way off. Resuming and finishing the entire task are different.
Is next month the completion time in 工事は来月再開する予定です。?
Show the answer and why
No. It is the scheduled time for resuming interrupted construction. The completion time is not given.