Regarding the age old conundrum of the tree falling in the forest. According to Barclay, there is no sound if there is no mind to hear it. I am thinking that there may be no human around hence no human auditory organs to absorb the waves and send the message of "sound" to the brain.....but that is a bit anthropocentric. The forest is full of creatures that have auditory organs, so some brains will hear the sound....some minds will perceive the sound of a crashing tree, no? (listening to Nigel Warburton's A Little History of Philisophy)