"I regret to say that this discussion seems to have deteriorated into solipsism from clayto and postmodernist waffle from whitecraw. And a falling tree makes a noise, even if there is no-one there to hear it; what we mean is that it's fall causes sound waves in the air that would be detected by a human ear, were one there to hear it. I refute you thus! As Dr Johnson nobly demonstrated." - George Jelliss, thank you!!!