Of all the questions I receive specifically about my paintings, the one I probably get the most is "why do you paint your mermaids with legs that transform partway down into fins?"
My answer is, why isn't everyone else?
Let's think about it. Mermaids are usually portrayed with breasts, which doesn't really make sense since they're not mammals, but they also probably shouldn't have hair or skin like ours. Obviously we're not going for the full fish here, or they'd be a lot less pretty to look at and would probably look like Lord Voldemort with fins.
Let's take a moment to imagine that, shall we?
So, we should probably try to make them a realistic cross between both. We have breasts to feed our children, and we don't have hundreds of them at a time, so clearly the mermaid is going to need some uh, reproductive abilities outside of laying eggs.
How does the traditional mermaid eliminate (that's fancy-talk for go wee-wee in the ocean)? How does the traditional mermaid reproduce? Are we supposed to assume she lays eggs like a fish and the boobs are just for looks? That doesn't make sense. Maybe she strips her tail off and has legs underneath? Why does she live in the water then? That doesn't make sense either.
Now, truthfully, a half human-half fish creation doesn't really make sense, either, but I think it's okay to try to find some realism in there somewhere. So I try to paint my mermaids in a way that makes some sense, plus it's more fun to paint them that way. Sometimes I even give them webbed fingers and ears, gills, or, you know, wings.
Really, though, they're a mythological creature and the way you portray them is entirely up to you. I paint them the way I paint them because I think it looks more graceful and natural, but other people prefer to paint them à la The Little Mermaid, and that's okay, too.
You do what you want. You're an artist!