The Subjectivity of Music
The musical quality of music is a property of music. It is not an important property of anything else that isn’t music – even though we may occasionally encounter other sounds in the world that we perceive as being somewhat musical, like a bird song, or even a repeated banging noise.
Our perception of the musical quality of music exists, apparently, as a perception of something where that perception is defined and implemented inside our brains.
Now everyone’s brain is different – we know that there are many different types of genetic variation that affect personality.
Indeed human beings are Homo economicus – that is, we live in societies where individual members can specialise in doing certain things that they are better at than other people. And the way to be a specialist is to have a brain that is a bit different from everyone else’s. So evolution wants us all to have different brains.
Also everyone’s brain is affected by different life experiences.
We know that our tastes in music are at least partially determined by which music we are actually exposed to in our lives.
And yet, despite all these causes of variation, and despite the fact that the perception of music does not relate to any important aspect of objective reality, there is substantial agreement between many people about what is and what isn’t music. In particular, there are many well-known musical items which most people will agree are music, as long as those people have been exposed to somewhat similar musical items previously. In the modern world, with music being almost freely available to everyone for free on the internet, there is substantial overlap in what everyone is exposed to, and for any given item of music there will be thousands of millions of people who will agree that that item is indeed a musical item.
Intersubjectivity
There are various terms used to describe what lies between the objective and the subjective, to refer to things where everyone has their own opinion but at the same time there is enough agreement between different people that there is a presumption that perhaps everyone should have the same opinion, and that some kind of objective reality underlies one’s own subjective opinion about the thing.
One such term is intersubjective. This can be used to describe those things that seem subjective, and therefore private to each individual, and yet there is substantial agreement between different people, thus the “inter” prefix.
There is also the phrase Subjective Universality, coined by the philosopher Immanuel Kant, where “Subjective” refers to the private individual’s subjective experience of a thing, and “Universality” refers to the fact that there is widespread agreement about the thing.
One significant example of intersubjectivity is morality. We all have different opinions about what is right and wrong. And yet the notions of right and wrong serve a function in society only because most of the time most people agree about what is right and wrong. And society as we know it could not exist at all without that agreement.
We could say something similar about music. There’s the private judgement, and some degree of agreement between different people, and the feeling that maybe it represents some kind of underlying objective reality.
However music does not seem to have any essential function like that of morality.
People make music, and people listen to music, and those can be fun things to do.
But some people aren’t interested in music at all, and they manage to live without it. (In contrast, there are people who are not interested in morality, but they are likely to end up in jail, or something worse.)
We could imagine a human society without music, and it would function perfectly OK, and we wouldn’t be too sad because we could make do with other forms of entertainment.
Evolution and Natural Selection
In the case of morality, it seems reasonable to assume that those factors which contribute to an individual’s sense of morality are factors which natural selection will select for.
In the case of music, the degree of intersubjectivity is sufficiently high that we could conclude that evolution has also selected for that.
The only caveat, in the case of music, is that the thing being selected for, at least in the modern world that we live in, apparently serves no useful function.
But, maybe sometime in the past it did serve a useful function.
That is, music used to be a thing where it mattered that there was quite a lot of agreement between different members of a society as to which musical items were musical.
And now, for whatever reason, it no longer matters. But the mechanisms of determining which musical items are musical or not musical continue to exist.
For a more detailed theory of how this could actually have been the case, and why music might still exist in some form that no longer fulfills its original purpose, see https://blog.thinkinghard.com/blog/the-circular-definition-of-music/.