What we define as music is a mental content generated by the ears and the brain, responding to external vibrational stimuli. This stimuli cause the musical perception, but are substantially different from it. Being each individual unique, cerebrally and psychologically, each one has its own particular way to respond to the external stimuli, having thus a more or less different experience from the listening of a same music piece. It's not possible to express objective and absolute judgements about a tune, not existing a reference version of it; in a certain sense there are as many versions as there are listeners.
PART 1
I think that what we call music, and its beauty (or ugliness), exist only in the subjectivity (this means in the minds) of the listeners.
In my opinion, the "sonic" vibrations external to us (e.g. those caused by an orchestra), being only air (or other material) in movement, don't have anything in common essentially with the sounds we hear in our subjectivity, which we define as "music". Music is in my opinion generated by the brain from external stimuli, and since aesthetic sensations are in my opinion based on our mental musical content (so not on the external stimuli which cause it), I think that also beauty (or ugliness) is inside us and not outside.
The fact that when listening to music one has the impression that the sounds are outside of us (except when using headphones), is in my opinion a kind of mental illusion.
I make a parallelism to try to clarify my idea: let's think about a cinema screen; it's a plane surface, but when watching a film projection one has an impression of depth (tridimensionality), as if there would be something beyond (behind) the screen. But we see only the screen. In a similar way I think we see images (and hear sounds), perceiving them as if we would see (and hear) them directly outside of us (in a tridimensional space), while in reality we are observing (and listening) only contents of our mind (the screen). And in my opinion this contents don't reflect exactly what is outside (as in the case of the sounds which we hear internally, which are stimulated externally by simple air in vibration).
This kind of illusion cannot in my opinion be avoided, because it depends on the profound functioning of our brain, but one can be aware of it.
I think furthermore that each "music piece" (in reality, as I said, simple air in vibration, if the term refers to what is outside of us, and which musically stimulates our minds) gives rise to different sensations in each listener, and in each listener at different listens, and thus that each individual has his particular (and changing) aesthetic sense.
With "aesthetic sense" I mean the way to perceive something as "nice" or "ugly", in varying degrees. To make a parallelism, I intend it a bit like the sense of taste, which can give perception of something as "good" or "bad", also here in varying degrees.
To be different I think is not only the aesthetic sense, but also the various impressions that one has of the various elements of a tune, impressions which I don't consider to be necessarily bound to a nice-ugly binomial.
Why do I believe this? My ideas were perhaps born empirically (i.e. through experience):
I hear expressing, from different persons, comments (on aesthetics and on own listening impressions) about a single tune which can be very different. I have moreover experimented on myself (getting later response also from other persons), that the way of perceiving a single tune, by a single person, varies over time.
If the aesthetic sensations (as explained above) and the impressions (for the same reason) don't refer to something external to the listener (air in vibration, etc.), but refer directly to his mental content, this indicates to me that the way of perceiving a tune (or better the external vibrations) depends on the biological structures (and if you want also the psychological and spiritual structures) of the listener (ears, brain, etc.), which create that mental content (responding to external vibrational stimuli, which as I said I wouldn't define as "music", but rather as that which causes it).
I think, I believe you'll agree from your experience, that sometimes also the environment (at a visual level, temperature level, social level, etc.) in which the listening takes place, has a certain influence on the listening. But also here I think that the biological and psychological structure of the listener enters into play, which creates the mental representations of the environment (and the sensations bound to it), responding to the external stimuli (visual, social, etc.), influencing in turn also the musical perception.
Excluding chance, which in addition to not knowing if it exists, I believe would make the listening chaotic, something which seems not to happen to me, I think that the human biological and psychological structure, and the listening environment, are the determining factors in musical perception (if you know others, please let me know).
My idea that each individual has its particular way of perceiving music, I demonstrate it to myself like this: being several persons in the same time and place listening to music, it can happen that some of them have very different listening experiences (judging from their comments and reactions). Being their objective listening environment very similar, this can't in my opinion justify this discrepancies. I explain this difference determined for the major part by a diversity of biological and psychological structure (the only factor remaining), which determines their aesthetic sense and the impressions which they have of a tune, making different for this listeners the way to perceive music (and the environment).
Thus, generalizing, it is in my opinion very improbable that two or more persons can have identical listening experiences of a tune, being very improbable the existence of two identical human beings (even only in the structures interested by the musical listening), even in different moments (I exclude also twins, which can be very similar in appearance, but which are in my opinion however cerebrally and psychologically different, having lived different experiences).
I think that also for a single individual it is very improbable to have identical listening experiences -- in different moments -- of a single tune, being he subject (I think you'll agree) to continuous changes, and he is never the same as he has been in the past (and I think that also the most "little" experiences can modify something, maybe often of little importance, but however in my opinion enough to make my reasoning valid).
Thus, when two persons discuss about the value of a tune, I think they're in reality speaking of two different tunes, as each of them has perceived them. I think that after having written a piece, if it gets listened by 50 persons, in a certain sense I have caused the generation of 50 different tunes.
So I usually take into consideration in the same way the point of view of each one, because I don't believe that there's the one who is able to listen better; I believe that each one listens to what his (unique and particular) brain proposes, and there is no objective beauty or ugliness, that could be picked, out of the minds.
I specify that with objective I mean "related to the object, intrinsic and concrete characteristic of it". While with subjective I mean "related to the conscious mind, present inside the mind and not outside" (this are my definitions).
I personally consider to be objective also that which is subjective perception, so namely content of our mind. That because our sensations, emotions, etc., are in my opinion concretely present in our mind, and we make direct experience of them. I'll make an example to clarify (this apparently strange idea): the sensation of warmness is present only mentally, thus it is subjective, but it is an intrinsic and concrete characteristic of that mental content, of which we have direct experience, thus it is objective at the same time.
It's also true though, I believe it based on my experience (of listening and confrontation with other persons), that between different listeners there can be some similarities in their aesthetic sense and listening impressions, thus one tune could touch them similarly in some aspects. So I, when I compose, compose according to my taste, but have the hope to find people who are near me musically.
I personally think that when the major part of the people, or even all of them, judge something (e.g. from an aesthetic point of view) in the same way, it is not suitable to use the term "objective". I rather prefer to use the term "shared". For example, if a tune is liked by everybody (or better said, everyone gets pleasure from the musical perception caused by certain groups of external vibrational stimuli), I wouldn't say that it is objectively nice, for the reasons which I have exposed in this present text, but would rather say that all the listeners share a same positive sensation/impression of it (or better said, they all share a positive response to those vibrational stimuli).
I add some curiosities regarding aesthetic sense, which I discovered and which other persons have confirmed, and which you perhaps didn't notice (like me before): often, when listening to a tune for the first times, it doesn't tell me much; let's say it can seem "flat" and little interesting to me. At subsequent listens I begin to like it, and I can even like it a lot. Sometimes it happens that I like a tune, and then discover that I had already listened to it, a fact that I didn't notice during that last listen (perhaps I had listened to it long time before, but this happened also in a matter of a few days). It seems to me thus that repeated listens of a tune can make us like it, maybe mostly melodically.
I'm not saying this is an absolute rule, but this happens to me (at least currently) very often. Then, maybe, judging from the vague remembrances of listening experiences which I have from my own infancy (but I'm far from certain), this could be different for a child; it could be that a child, listening to an unknown tune, could find it nice and stirring already from the first listen, if this contains some musical elements which are a novelty for him, and thus impress him particularly.
PART 2
I add something regarding the issue of quality.
I often hear people replying to my ideas exposed here above, that if the beauty of a tune is subjective, there's still its quality to take in consideration, which should be something objective, intrinsic of a given music (if my interpretation of this idea is correct).
With "quality" -- seems to me -- are usually intended such things as (remaining in the music field) a good touch, a good expressivity, a good sound, a good technique, complexity, and more.
I think, first of all, that the discourse from before is valid here, too, namely that air in vibration (or more upstream a string or a percussion, vibrating) are essentially different from what we perceive and call music, and consequentially from its quality (good or bad), as this last one refers to the mental musical content (and not, I repeat, to air in vibration, etc.). A question to pose to oneself could further clarify the concept: where is it situated, the quality which I perceive? (Think about it!)
In my opinion, quality is not only confined in the minds, but it is neither a real perception. In my opinion, it is nothing more than an abstract concept to define the presence of certain aesthetic sensations (at least in the case of music). I think in fact, that something which gets judged as being of "good quality", is judged this way because it is liked under certain aspects. To indicate touch, expressivity, sound, technique (etc.) as being of "good quality", means in my opinion that there's something about this categories, or to their effects, which is liked (it is nice, at least for who affirms it), or vice versa. For example, I think that saying that a guitarist has a good touch, doesn't mean that his touch has such a thing as "good quality" in itself (after all his fingers are just pieces of matter in motion, I believe), or in the perception which I have of it, but rather that I like the sound which is caused by his touch. If we wouldn't like the sound, we wouldn't say that he has a good touch, I think. It seems to me, thus, that the concept of quality (at least in music) is to lead back to aesthetic sensations (and consequently to the first part of my discourse).
Some words in particular for the concept of "complexity", with another question to pose to oneself: when does complexity begin, and when does simplicity? My answer is that, missing an objective border, both categories come to fall (though they can still be useful to communicate in the everyday life).
Furthermore, and I think that this counts also for other concepts (e.g. for those of originality and traditionality), I believe that it is no absolute rule that complexity (as subjective concept) is better than simplicity (still as subjective concept). In my opinion it is a matter of culture and personal preferences.
All this discourse about quality -- in this second part -- doesn't mean, in my opinion, that for a musician it is needless to be concerned with this musical aesthetic categories (touch, expressivity, sound, etc.); I'm of the idea, as explained before, that the aesthetic sense of a musician can be shared (partly) by his listeners, and I think that if he likes something, there's more probability that this will be liked by someone else, as opposed to something which he first already doesn't like.
