:See Diodorus Cronus § Master argument for the classical master argument related to the problem of future contingents.
The master argument is George Berkeley's argument that mind-independent objects do not exist because it is impossible to conceive of them. The argument is against the intuitions that many have and has been widely challenged. The term "Berkeley's master argument" was introduced by Andre Gallois in 1974. His term has firmly become currency of contemporary Berkeley scholarship.
Overview
In order to determine whether it is possible for a tree to exist outside of the mind, we need to be able to think of an unconceived tree. But as soon as we try to think about this tree, we have conceived it. So we have failed and there is no good reason to believe that trees exist outside of the mind.