It isn't a circular definition that he's giving so much as reductive (i.e. not high cultural). The reason I think you definition fails is that it ignores popular music in most of music history. While this would often be called folk music I think there is certain stuff that was regionally very popular and did not require a middle class to consume it or indeed that the artist make very much at all. This music was literally popular but did not require a middle class. Conversely the more useful definition in my view is the stylistic one. Music emerging not from higher cultural trends (so called art music) but from the people generally (folk music) and those things that are derivative from it. The popular music you speak of is music that comes from these roots (and very specifically southern poor black roots and to a lesser extent southern poor white roots). This stuff is popular music regardless of whether it is actually popular in and of itself. In order for it to be widely disseminated I'll grant you a middle class is required (or at least a class with disposable income).
I'm not saying the music has to be purchased by some certain amount of people to qualify as pop. I didn't think I had to spell out the element of intent
. Folk musicians from times gone past had no intent of being sustained by performing music and did not view their listeners as customers. I'm sure we could go through the history of street performance and find intent and call it pop music. But even then, without a fixed venue for consumption, there still is a very limited "pop culture."
Now, second, you say "the more useful definition is the stylistic one." Stylistic, as in, the aesthetic definition? Because I hardly see how you could argue that an aesthetic definition is more useful
than an economic one. That's a baffling assertion.
Contrary to your claims, the pop music I speak of comes from BOTH folk roots AND elite roots. It's the mixing and constant remixing of both, which occurs because of the money involved. And so that gives us three broad genres. Obviously you will still be able to go and find artists that straddle the lines, but there's nothing wrong with that.
Pop music is a mixing pot of music from both folk and elite origins, which plays out in a commercial market. This is just a different way of saying pop music is music supported by a broad base of customers.
Re: innovation is about cost reduction and my original post… I haven't actually done the research to write a graduate thesis on this thing, but many revolutionary styles have three things in common at their inception: 1. cost reduction, 2. radically different from existing styles, 3. targeting a neglected audience. Most frequently, the neglected audience was young black people. Basically it's disruptive innovation, which is a prominent business buzzword that I don't want to sit here and talk about.