There once was a man who said: "God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one about in the Quad."

Notes from Wikiquote

The topic of this limerick and the following one is George Berkeley's philosophical principle, "To be is to be perceived".

The Hidden Stream (1952)

Quote text and notes from Wikiquote: Ronald Knox (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.