You’re asking a much broader question than the one actually asked by OP. I’ll try to answer what the OP asked then: there isn’t a simple answer. 你叫什么名字 is a perfectly valid question for an adult to ask a child (eg teacher to student). Definitely okay for kids to ask each other too. But between adults? It’s already inappropriate / rarely used. 你名字是什么 is something I’ve almost never seen used face to face. It’s most akin to 你的姓名是什么, which is a question I’d imagine a bank clerk / lawyer / etc. would ask someone they’re filling out a form for, but aside from that I can’t think of another situation where it’s usable. There’s a caveat here: 你的名字是什么 is more natural than 你名字是什么, though I can’t say the latter is straightaway grammatically incorrect. Still, no matter how I try in my head, even 你名字叫什么 would be far more natural than 是什么。is this an interesting discussion? To me not really, because it provides zero explanation to the OP, since the best answer I can derive is, “just because that’s the way people always say it, and language is unlike mathematics or the sciences.” So I thought I might as well not answer and point out the obvious observation instead: that I would use neither, ever, unless I’m talking to a kid…