pseudo-names

Family members have names, obviously, but they also have sort of pseudo-names - the kinship terms we call them like 'Mum'. I've actually always called my parents by their first names and also my maternal grandparents, who I always called Paul and Rosemary. My paternal grandparents, on the other hand, are Grandma and Grandad.

Now these kinship terms are normal nouns when you're talking about them, and occur with a determiner (usually a possessive determiner, as in my mum). When you're using them as a term of address, though, they work like a name. So just as you don't say the Louise or my Jane, you just say plain Grandma when you're talking to them as opposed to about them.

It turns out that I have inadequately acquired the rules about this. When I'm talking about my grandma, I'll often refer to her just as 'Grandma'. So I'll say something like Grandma sent us a Christmas card today. This apparently sounds a bit odd and I should say My grandma sent us a Christmas card today in order not to sound like she's also the grandma of the person I'm talking to. I think that because all my other relatives just have names, I treat 'Grandma' as her name and use it accordingly: compare Rosemary sent us a Christmas card today, which is totally normal.