I considered Herakles a legend, because it seemed plausible to me that some hunky bloke had stomped about Greece, knacking lion and cleaning up horse shit. But Pegasus was a myth because a horse with wings feels pretty unlikely.
There's something in this, in common usage. Calling Hulk Hogan a legendary figure in wrestling reads well, but calling him a mythical figure... like he doesn't really exist. But he does, and he's even got a sex tape which I'd rather give a miss.
What I didn't consider is how the mythical and the legendary are weaved together: parts of The Twelve Labours of Herakles feed on the bunkum: that business with his dad being Zeus? The snakes in his cradle?
When I studied Religious Education as part of my teacher training, I came across a new definition of myth. Myth was 'a story with meaning'. For the first time, I claimed I had a methodology, and that was to use an idea until it breaks, then build a new idea with the left-overs and bits of the idea that broke it.
This version of myth makes no claims about the 'truth' of a story,
Hulk Hogan is still a legend, but now there is a myth of Hulk Hogan. It's probably got a moral of some sort - maybe that it's not a good idea to say racist stuff if you are a celebrity.
The difference between my two definition of myth isn't necessarily commonly recognised, and the idea of myth as a bogus story is often how it is used by people who aren't trying to be smart-ass post-modernists. I prefer another word for that kind of story: bullshit.
But when I say 'myth', don't be insulted. I am saying that it has meaning, but I am making no value judgement about whether it is 'true' or 'false'. Or whether it means anything to me.
This'll give you a headache, while I think about why I have this definition of myth, and why it matters...