“As an idealist, Berkeley believed that nothing is real but minds and their ideas. Ideas do not exist independently of minds. Through a complicated and flawed line of reasoning he concluded that “to be is to be perceived.” Something exists only if someone has the idea of it.
Though he never put the question in the exact words of the famous quotation, Berkeley would say that if a tree fell in the forest and there was no one (not even a squirrel) there to hear it, not only would it not make a sound, but there would be no tree.
The good news is, according to Berkeley, that the mind of God always perceives everything. So the tree will always make a sound, and there’s no need to worry about blipping out of existence if you fall asleep in a room by yourself.”