I've written previously about the idea that most definitions are centers, not borders. In brief: we often get ourselves into semantic, legal, and ethical tangles by pretending definitions specify a conceptual boundary into which a thing either does or does not fit, but while this works in some places, it often doesn't work and causes problems.
Is this a car? When the choice is between a Toyota Corolla and a bicycle, the question is clear; but there are plenty of other things that lie on the borders, like a partially disassembled car, a Terrafugia Transition, an El Camino, a Trev, etc. Even the legal definitions that are promulgated by DMVs and state legislatures often fail as advances in technology create new things that the old definitions didn't account for (sometimes as an intentional attempt to sidestep legal limitations: many "smart cars" are three-wheelers for no other reason besides avoiding some of the safety requirements on cars in state laws).
In most cases, we would be better served by assuming definitions are of centers rather than borders. There's a center of the concept of a car that can be typified by something like, say, a Toyota Corolla; and the nearer something is to that, that is, the more like it that the thing is, the more we can call it a car. The point is there is no single, widely agreed upon demarcation at which things stop being cars. While we might still disagree about what is at the center, and where we stop using the word, the concept of dealing with definitions this way saves us from falling into the trap of imagining that there is, or even that there should be, agreement about these things. If your concept of "car" has its center on the Pontiac Mustang, that might differ from the person whose center is the Toyota Corolla, but not enough to cause the kind of intractable disagreements that tend to grow out of definition-based debates (like the abortion debate).
This point is central (no pun intended) to the debates about taxonomy, and crops up in the schism between cladists (who strive to make taxonomy reflect evolutionary heritage directly) and other taxonomical approaches, as well as in the splinters amongst cladists. A recent discussion about the innocuous subject of the song "Sing Sing Sing" on my Facebook page made me realize that the taxonomy of musical styles has the same considerations -- you could even argue about structural versus cladistic taxonomy (because parallel evolutions into similar styles maybe should or maybe shouldn't be grouped together). Though with music you have a big problem that biological taxonomists don't have: cross-breeding between cladistically distant parts of the taxonomy is not only common in music, it very commonly creates new forms, so you couldn't make a tree, but only a tangled, unhelpful web, if you insisted on staying cladistic.
There's a temptation, which one of the posters flirts with, to abandon the value of taxonomy entirely, but this is mostly based on the standard problem of definitions being centers but treated as borders. You can't ever make a border-based definition of what constitutes "classic rock" or "boogie woogie" that is immune to the problem of people disagreeing about whether this band or that song fits into it, because the whole approach, of defining based on borders, is flawed. However, you can certainly make a list of ten songs such that almost anyone would agree that all ten are definitely classic rock, and definitely sit near the center of what classic rock means, and thus convey accurately and usefully a definition of classic rock that isn't plagued by controversy since it doesn't focus its attention on the areas of contention.
So R&B can be divided up into its many children (whether cladistic or structural), and somewhere in that big mess of styles you will find "big band swing", which (I posited) has its center on the song "Sing Sing Sing" (I further suggested Louis Prima's performance, though a strong case has also been made for Benny Goodman's performance at Carnegie Hall). Somewhere nearby stands "boogie woogie", but I didn't agree that the Andrews Sisters singing "Boogie Woogie Bugle Boy" can be its center because boogie woogie is too big a category; "Bugle Boy" is definitely the center of one of its subdivisions, but boogie woogie seems to me to include a few styles too dissimilar to that song for it to represent them, such as some ragtime and barrelhouse music. I'm not sure what the name is for the style that that song does typify, though it's clearly at the point of intersection between boogie woogie and swing.
That's not incidental, though. That's the whole point. There's a definite style that you could identify which can be best defined by its similarity to "Boogie Woogie Bugle Boy" but which may or may not have a widely accepted name. The fact that it has a definitive center, a Platonic ideal, demonstrates that it does exist conceptually as a category. More importantly, the value of categorization itself is not limited by the fuzziness of the borders -- you just have to stop focusing on the borders.
(The question of whether naming, or as it's usually called pejoratively, "labelling," things, is inherently a destructive or limiting act, is a whole other philosophical subject about which I have written and will no doubt write again.)