Back again.
I just glanced at my previous post. What a jumble... I don't know why the formatting turned out like that. I apologise to everybody that read it.
Anyway, I asked for definitions and I got them from William and Macker. Since you guys went into the trouble I will add to my already long diatribe. But first, I just want to say that I mentioned my writing a book because I feel it chimes very well with this discussion. When it is finished, I will investigate whether there is any interest to be generated in publishing it, but that is more than a long shot. I realise this. If it doesn't happen (which it most probably won't - the book market is much more saturated than the music one), I won't wail at the world for being too stupid and heathenish not to be paying attention to my "brilliant" short fiction, and I know that the publishers who will reject me will vie ferociously for the rights to a Kardashyan autobiography. I don't care (too much). I am writing these stories because it gives me pleasure. I get pure enjoyment out of writing, as a hobby, as others get out of writing music, as a hobby. Id est, without the pressures that are automatically applied to a professional.
I perused a lot of the posts here, and the prevailing idea is that a professional composer is one who makes money from their music. Well, yes and no. The money is actually the last factor in the equation. One has to satisfy every other requirement of the "job" in order to ever get to see any money. It is very akin to being an accountant or a plumber when it comes to that. People that pay money have certain expectations from the benefiting party. The whole transaction is expected to be equitable. People will rarely use an accountant or a plumber that is not referred to them by someone they trust. The times that they do go outside their comfort zone -during an emergency- they do so with fingers crossed. For the accountant they will expect that he is certified by some authority they recognise (jsg made a similar point), and this will also apply to music professionals. It is not enough that you even get access to somebody, you will play them a couple of your tracks, they'll like them and then they'll bring out their check book. Not if they know what's good for them (see point above regarding references).
Ability to write music that people like is not nearly enough in itself to make you a professional. No-no! Actually, it is not even necessary. What people that are prepared to give you money want to know is whether you can compose music to their requirements, not your own. They want to know that you can compose to at least an average professional standard for the kind of ensemble they have in mind. This is not a simple criterion: Is the ensemble professional or amateur? Do you know how to compose for professionals and amateurs for all instruments? Do you know what the differences are in range, instrumental technique, compositional technique - are you going to give multi phonics to a high-school woodwind ensemble? Etc. They want to know that you can complete the music on agreed schedule(!) and idiom, and that you will present them with score and parts of professional standards (this goes 2x for amateurs - i.e. not what the Score Editor of your favourite D.A.W. will hurl out). I am omitting a score of other important details.
What is it that will reassure these people commissioning you that you will deliver a professional product? The fact that your mother and Facebook/Youtube friends 👍like your music? A joke, surely. First of all, a university degree is that aforementioned authority people will accept as an initial guarantee that at the very least you know the rudiments and that you have already been proven responsible enough to deliver adequate work to deadlines. They cannot wait until inspiration hits. This is another difference between professionals and everybody else. Professionals have to compose, no matter what! They have contracts and a reputation to uphold/build, negotiating an unfriendly environment of vicious and back-breaking competition... If you think all the aforementioned skills can be acquired overnight, I know which category you don't belong to. Professional composers are not "merely" musicians (good or bad). They are excellent time managers, entrepreneurs (look up the origin of this word - you won't believe it...), promoters, and -most of all- reliable.
If one satisfies all requirements of being a professional composer, then -at last- money will find its way into the conversation. How much of it will depend on the client. The client will of course get the best professional he can afford. This is where it gets a little fuzzy, in that the most expensive composer is not necessarily the best. That is another point that I feel has not been addressed: The vast-vast-vast majority of professionals, in any field, by statistical definition, are journeymen! And these are the ones that know their stuff! Not the dilettantes, the hobbyists, etc. They are as journeymen as your accountant (who is not Warren Buffet's accountant I presume).
It is not by chance I mentioned Sorabji in my first post, asking rhetorically whether he was less or more professional a composer than Hans or J. Williams. You learn about Sorabji at university if you study composition, and maybe more than in passing (you learn nothing about Williams, let alone Hans). An incredible iconoclast, contemptuous of both atonality and neo-classicism, with a profound, complex thought that translates into hours of music for each work (his Piano Symphony n.5 "Symphonia Brevis" lasts over two hours), Sorabji was so eccentric that he reached a point where he summarily forbade any performances of his works without his explicit permission. The combination of the over-protracted, complex nature of his music, his introversion and misanthropy resulted in an absolute scarcity of existing recordings of his music. His extensive symphonic works have never been recorded insofar as I know. Apparently, there are also some orchestration mistakes that have been noted in his interminable manuscripts, but these, surely, would have been corrected if he ever intended to publish. Be that as it may, there they are.
Conclusion: Sorabji was not a professional composer, certainly not in the league of Hans and J. Williams. Music history however has immortalised him as an 'artist'.
'Artist' is yet another term, which I posited in my second post, the one that matters to me, and the one with which I will close this post.
All the other designations are more or less claimable for oneself. You can call yourself an amateur, a dilettante (which didn't have such negative connotations in the past; what happened?), or a hobbyist, most will just take you on your word as the range is just so abysmally vast. If you call yourself a professional to anyone 'in the know' at least, you'd better be able to back it up [do you get commissioned a lot? For money? By whom, etc. This will determine whether you are a journeyman professional (99.999%), further details (fee, prestige of commissioning party, etc.) will determine whether you belong to the high or low end of the journeyman spectrum, or in the infinitesimal margin above or below it].
(Musical) 'Artist' is the only designation that you don't get to claim for yourself. It is a really rare distinction and must be bestowed upon you by somebody else, either by other artists or professionals, or by people with real, vast musical culture. Not by friends and family. Not by fellow amateurs.
I'm going to bed. I bid you all goodnight, and sweet dreams...