how do I write a good tune?

And of course the answers to questions like "what makes a good tune" and "what tunes are good" are going to be extremely moot.

I kind of expected that response. I have some musical theory. But I can't help noticing that a lot of music from people with perfectly good musical training isn't very tuneful to my ears. So there's got to be more to it than that.

" It would basically explain all you want to know, in probably a more authorative fashion than ILM can"

But I'd like to hear the ILM version rather than the standard story. I'm curious about the idea of melody here.

"And of course the answers to questions like "what makes a good tune" and "what tunes are good" are going to be extremely moot."

Probably true. I'm also open to hearing different sides of a debate about whether there's an objective truth to the matter. For example, do all the song-writing courses teach the same thing? Or are there different schools with rival ideas, and what are the outputs from the different theories?

And, no, musicall theory may not neccessarily help. Listening to lots of generally acclaimed songs will help a lot more, as good songwriting has always been about stealing, although in a creative way.

this is bullshit. no creative act is "congenital". being creative is a learned skill, just like anything else. You have to train your mind to do it.

No. Certainly not true. It is a learned skill, as Shakey said. Some people do it better than others, but that is because of a certain training that have made them able to do so. For instance, Wolfgang Amadeus Mozart, who is sort of the master of melody, may not have had the healthies childhood you can imagine (no "Wunderkind" had that), but I guess his extremely early music upbringing helped him think tunes in a way that most people don't. His talent was still learned though, which is something virtually all musical talent (except a good singing voice, which may be something you possess from nature) is largely about.

And I read somewhere that Jobim, I think, would write his verse melody and then, when he got to the bridge, collect all the notes he hadn't used yet to write the bridge melody. Of course, I can't think of any Jobim songs that demonstrate this technique, so I can't speak to its efficacy.

And I think Paul McCartney's goal in writing "Paperback Writer" was a melody that consisted of one note. Which didn't exactly happen, but it's another example of using constraints. You may stumble upon a good tune every once in a while, but it's DEFINITELY something you can achieve through hard work, as long as it doesn't sound like hard work, but that's true of anything you construct.

What nonsense. Beethoven had two brothers, who were brought up in the same environment as him, but I doubt you could hum a tune by either of them.
If it really were the case that compositional ability were just a function of exposure to music, the millions of people around the world who are the products of households that are appreciative of music, and who study musical instruments from their early childhoods, would all be churning out masterworks to rival those of the greats. The reality is however that most of them don't originate any music in their entire lives, because the inspiration isn't present.
Mozart himself once wrote, "I write as a sow piddles" - by which he meant that the music flowed effortlessly and copiously from his mind and hands. Obviously, if he had never been taught to play an instrument, his vast talent would most likely have remained untapped - but to suggest that his remarkable body of work could have been produced by anybody who just worked hard enough at it is absurdly reductive.

Which may be the result of one of these

1. His brothers were just as talented as him, but got sick of being raised as "Wunderkinder" and chose to do other stuff instead of music
2. His brothers were just as talented as him, but coincidences meant their work is generally forgotten now
3. His brothers didn't manage to utilize their upbringing the same way, and as such, never equalled his talent
4. His brothers, already during growing up, didn't have a lot of motivation for music the same way Ludwig did, and as such, they never learned as much as Ludwig.