Suppose an alien civilization does archeology on us and tries to figure out what music is. Suppose this civilization has culture of different kinds but does not have the sense of hearing. Biologically speaking, these creatures simply lack ears. Intellectually, they can figure out that music has to do with vibrations of air perceived in a particular way, but they would not ever possess music experientially.
They could develop theories. Some would see music as a branch of mathematics. Others, as a system of cultural prestige or a strange adjunct to sexual selection. There would be debates about what music is, with whole schools of thought standing in opposition to one another. There would the economic musicologists, the mathematical musicologists. The only thing there wouldn't be would be the musical musicologists.
Until one day, a young scholar under the sway of the mathematicians wakes up one day with a kind of epiphany... Yet this person's theories can never be accepted: they are based on accepting as real something that everyone else agrees is a kind of phantom: sound itself.