Alvin asked:
Did bishop Berkeley actually write the question if a tree fell in the forest and no one was present to hear it, would there be a sound?
Answer by Tony Fahey
Yes Alvin, it seems that Bishop Berkeley did raise this question. It should be understood that George Berkeley’s central thesis is that all we can ever know about objects is merely the ideas we have of them. According to Berkeley there is no such entity as a physical world, or matter, in the sense of an independently existing object. Rather it is that all that we ordinarily call physical objects are actually collections of ideas in the mind. The appearances we experience are the very objects and the appearances are sensations or perceptions of a thinking being. His most famous saying is ‘esse est percipi’ – ‘to be is to be perceived’. According to the ‘esse is percipi’ thesis, all the things surrounding us are nothing but our ideas. Sensible things have no other existence distinct from their being perceived by us. This also applies to human bodies. When we see our bodies or move our limbs, we perceive only certain sensations in our consciousness.
Using a series of arguments, often called by philosophers as the ‘veil of perception’, Berkeley argued that since we never perceive anything called ‘matter’, but only ideas, the view that there is a material substance lying behind and supporting these perceptions is untenable. For Berkeley everything was mind-dependent: if one cannot have an image of a something in the mind, then it fails to exist – hence his thesis ‘to be is to be perceived’. Berkeley’s response to those who argued that if there were no material substrate behind our ideas, how is it that things persist when no one perceives them, was to argue that all our perceptions are ideas produced for us by God. Thus, it can be said that in response to the issue of the tree falling in the forest, Berkeley would take the view that since God have conceived the idea of such a scenario, then God would hear it fall.
Perhaps I should add that one of the most ardent of the many critics of Berkeley’s philosophy was Dr. Samuel Johnson who is said to have famously refuted the eminent bishop’s theory of immaterialism by kicking a stone in the churchyard after one of Berkeley’s sermons exclaiming ‘I refute it thus!’
Answer by Craig Skinner
Not exactly. He says something more radical, namely:
‘The objects of sense exist only when they are perceived: the trees therefore are in the garden, or the chairs in the parlour, no longer than while there is some body by to perceive them’ (A Treatise Concerning the Principles of Human Knowledge 45).
For Berkeley, ‘to be is to be perceived’. Everyday objects, such as trees, exist, but are not made of matter (there is no such thing). Rather they are ideas. They exist in God’s mind, and sometimes in our minds.
For those of us who think material trees do exist, a tree falling in a lonely forest will produce a sound defined as ‘vibrations in the air able to be heard’, and won’t produce a sound defined as ‘sensation produced by vibrations in the air impinging on an eardrum’.
My wife’s version is trickier:
‘If a man speaks in the forest and no one is present to hear him, is he still wrong?’
Ask a Philosopher 
Since our perceptions very much seem to leave the impression that material objects do possess a physical existence (while acknowledging that the proposition appears very difficult to prove) what ‘evidence’ did Berkeley think he had, to justify denying it?