拍子

1. Origins, structure, and basic meaning

• Structure: 拍子 (ひょうし) is a noun for musical beat or meter. 拍子に合わせて sets a standard for movement, while 拍子が変わる makes the meter the changing subject.
• Basic usage: The dancers move 拍子に合わせて; the difficulty of the piece comes from the fact that 拍子が変わる partway through.

2. Common pitfalls and similar expressions

• Standard for movement versus changing meter
  • With に合わせて, the beat guides the dancing. With が変わる, the meter itself changes; the first に is therefore not a simple destination marker.