AIBU to expect my boyfriend to know the difference between step and half siblings

I knew someone at work who used to talk about her step-sister. But when she gave more detail it turned out that the sister was a child her mother had before marriage and had been brought up by other family members, so biologically a half-sister not step. Step-sisters are related by marriage not biology. I didn't correct her but it shows it's not uncommon to make this error.

There's a lot of people who think the term half-sibling is rude or disrespectful in some way. Maybe it's a sensitivity about mum or dad having had children with more than one partner, I don't know. Technically/biologically it's a correct term.

But I also understand why it's easier and nicer to refer to your siblings who grew up in the same household from early childhood simply as siblings. I have noticed that this is particularly the case where the same mother is shared (though this usually also means same household!) I have a friend whose household siblings consisted of her and a "full" sister from mums first marriage and three half sibs from mums second marriage. I have noticed she refers to her household siblings as just brothers and sisters, never half. But her dad also has more bio children from his second marriage who she just refers to as "my dad's other children" as if she doesn't consider them siblings at all. Proximity has a lot to do with it I guess.

You could procreate with one but not the other 🫣 I think that's an easier way to differentiate between them, for those who don't understand the difference.

Why does it matter to you whether his brother is a half-brother or a step-brother?

Why? They’re not your stepsisters.

surely technically they are his nephews-in-law?

In the same way that your sister is his sister-in-law

I had a friend once who admitted he wasn't entirely certain of the definition of "cousin" - not second or removed or anything, just cousin - or niece/nephew or uncle/aunt

...because he'd never had any

Ok but in real life that relationship is nephew-uncle. Has anyone, anywhere ever referred to their ‘uncle in law’?

i didnt grow up with my step siblings
i referred to them as step siblings
turns out they are half siblings - i havent seem them for 28 years, understandably, the common denominator, our father, died 29 years ago

perhaps that is how they were referred to, by my dm ? who knows. i didnt make up the term as a child.

Lots of people do muddle them up, because it's not important to them. It's not that they don't know, it's just they are not thinking about it.

You can just explain why it's important to you, and he'll use the correct term from now on.

Not in English. In some languages, there's a separate word for an uncle or aunt through marriage. (Also separate words for an uncle or aunt on your mother or father's side.)

I still get mixed up, but in some parts of the Balkans, a blood aunt who is your parent's sister is 'tetka'; her husband is your 'tetak'.

A blood uncle who is your parent's brother is 'ujak'; his wife your 'una'.

I don’t know anyone who uses the term “half” in real life to describe their actually half siblings. They all just use brother/sister. I understand what it means but I don’t think it’s commonly used in practice. “Step” is used a lot though.

If you don't have first hand experience of step or half siblings then it might not be something you take much notice of as it's not relevant to you.
If you meet someone with a more complicated family set up than you, you may know who is related to who by birth or marriage once told but you might forget the correct terms because it doesn't directly involve you.

Darn it, I knew my hyperbolic inclusion of ‘anywhere’ might come back to bite me!

Sorry - I'm not always good at spotting hyperbole and I promise that I wasn't being snarky, in any case. I find that I'm not very good at conveying tone online. It was more the idea of "Here's an (un?) interesting fact."

I blame my OCD. feels compelled to add that she genuinely has OCD and is not being flippant

That makes sense. I saw that when I was teaching.

People are, to me, weirdly dense sometimes on stuff like this. But I'm like the systematising side of things, and not everyone is like that. I'm always bemused at people making out that second cousins is too complicated a relationship to understand. Plus there's the thing where some people consider 'half sibling' to be offensive somehow because it invalidates the relationship. It's just a factual thing to me. Sure it may not matter day to day and you may just say 'my brother'. But he's still technically a half brother if you only share one parent.

None of me, my wife, my kids, my sister, her kids, my parents, my wife's parents etc etc have step brothers and sisters of half- brothers and sisters.

I'm not sure I could confidently immediately know the difference.

Stepbrothers and sisters: the children of your new parent that aren't your blood relations.

Half-brothers or sisters: siblings where you share a mum or dad, but not both.

That's it, right?

It's a good job you're not judgemental, isn't it?

I can get there if I think about it, but it's an abstract concept rather than one I can hang names onto. I don't have friends with half or step siblings so it's not like I have an innate sense of Sarah and Louise are half siblings but Joanne is their step siblings.

On my mother's side I'm 4th generation only child. DH is the child of 2 only children. Siblings are a rarity in our family.
I'm also adopted so family trees aren't really my thing because I'm not related to anyone I know except my children.

Very true. So many people are confused by so many things these days. One could be forgiven for thinking they must be a bit dense.

Do you mean your mum referred to your Dads children with another partner as step siblings?
Did they have a good relationship at all? I have heard of women who won’t recognise the fact other parents other children as being related to their own.

To be fair I am genuinely surprised, I don’t know who told me but for example children’s books often refer to “wicked step mothers” or films/tv programs etc..

No reason to have a relationship from my DM point of view, I had a step mother so therefore I had step sisters, it is of no importance and genuinely not deep