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)?

The issue here seems to be verbal. It's not clear that ordinary language has a settled answer to the question whether "sound" refers to the vibration in the air, or to the experience that the vibrations cause. If we fix on the former, then there have been plenty of sounds that never led to any experiences. If we fix on the latter, then sounds and experiences of a certain sort are one and the same thing. But there's no deep fact about which is the "right" way to think of it.

Something else worth keeping in mind: language doesn't map onto the world in any simple, direct way, and in particular we need to be careful about letting the fact that we have the noun "sound" fool us into thinking that there is some thing in the world -- a sound -- whose location (in the head? in the landscape?...) needs to be sorted out.

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