CHAPTER 1 5
Ears and Hearing
When I was in the third grade, my teacher asked the class an oft-re-
peated question: if a tree falls in a forest and there is no one (no people,
no other animals, no beings of any kind with ears) around to hear it,
does it make a sound? I don’t recall how the question was answered at
the time, but I do recall being unsatisfied with the answer. How would
you answer it?
The answer depends on how we choose to define sound. If sound is
defined as a mental experience, then sound would require someone
or something capable of mental experience. According to our current
understanding of hearing, this means a being having an ear or other
sound-detecting organ, and a nervous system to process the signals
generated by the sensory organ. If, however, we define sound as vari-
ation in air pressure generated by the action of the tree falling, then
that air pressure variation presumably exists whether or not any be-
ings with ears and nervous systems are in the vicinity. Because sound
might reasonably be defined in either of these ways, it is necessary to
specify what one means by sound in order to give a coherent answer to
the question. Most dictionary definitions of sound conflate these two
possible meanings (mental experience and physical vibration), and I