今日の英語：If a tree falls in a forest,

Geicoの「みんなが知ってる」CMシリーズ。

GEICO Did You Know - A tree does make a sound ...

これは英語人の間では常識らしい。

"If a tree falls in a forest and no one is around to hear it, does it make a sound?" is a philosophical thought experiment that raises questions regarding observation and knowledge of reality.

If a tree falls in a forest - Wikipedia, the free encyclopedia

 今日のNPRの"Car Talk"でも出てきたんで、やっぱり"Everybody knows that"なんだろう。