Am I correct in thinking that vibrations in the air are just one cause of sound, and that really sounds are what are experienced? So for example under this definition of sound, ringing in the ears is included. Equally then, that sights can be caused by light bouncing off objects but also by the imagination? Can I draw the conclusion then that there are an equal number of sounds/sights/tastes/smells/feelings that have ever existed, than have ever been seen/heard/tasted/smelled/felt? The tree that falls in the woods with no one in it makes no sound at all (but plenty of vibrations)?