What does George Berkeley mean by the phrase “to be is to be perceived”?

George Berkeley’s famous doctrine, esse est percipi (“to be is to be perceived”), is the cornerstone of his subjective idealism. It asserts that for non-thinking beings, existence is entirely dependent on being perceived by a mind.12

Berkeley argued that physical objects—such as tables, chairs, or trees—are not independent material substances but are instead collections of "sensible ideas" or sense-data. Because ideas cannot exist outside of a mind, these objects exist only insofar as they are perceived. He rejected the notion of a material world existing "behind" or "underlying" our perceptions, maintaining that there is no third term between the perceiver and the perceived.12

While this may seem to imply that objects vanish when not being observed by humans, Berkeley clarified that he did not hold such an "in-and-out" view of existence. He maintained that objects remain in existence because they are continuously perceived by the mind of God. Thus, his philosophy was intended to align with common sense, defining reality as a relationship between active spirits and the passive ideas they perceive.12