What kinds of relatives do you have?
This seems like a simple question. But that’s because we take our words and concepts so much for granted that we don’t even realize the extent to which they’re a cultural construct. Yes, there’s biology involved . . . but our understanding of and way of talking about that biology is shaped by society, by which relationships we consider to be important enough to provide them with their own special words and which ones we don’t.
In modern Anglophone terms, you have a certain set of possibilities. Parents: mother and father. Siblings: brother and sister. Children: son and daughter. Parents’ parents: grandmother and grandfather, and then add “great-” as many times as necessary to mark previous generations; ditto for children’s children and so forth. Parents’ siblings: aunt and uncle, again with “great-” or “grand-” if you need to go up a generation to a grandparent’s sibling. Children of someone in the aunt/uncle corner of things: cousins.
We do get a little complicated where cousins are concerned, enough so that many people nowadays aren’t really clear on how those terms even work. The children of my aunts and uncles are my first cousins. The children of my great-aunts and great-uncles — my parents’ first cousins — are my first cousins once removed, i.e. one generation removed. So are the children of my first cousins. The grandchildren of my first cousins are my first cousins twice removed, because now there’s a gap of two generations between us. The children of my parents’ first cousins, on the other hand — who belong to my generation — are my second cousins. My kids and their kids will be third cousins to each other.
Not all languages bother with those kinds of distinctions. They may just lump everyone under the generic label of “cousin,” i.e. someone related to me in a fashion not otherwise defined. We do that in daily discourse, too, and also leave out another factor: while most of our kinship terms are paired by gender — mother/father, brother/sister, aunt/uncle, and so forth — we have only the one bare “cousin,” with no specific terms to differentiate girlcousins from boycousins. In a language with gendered nouns, on the other hand, that might be inherent; in Spanish I have to specify whether my cousin is a primo (male) or prima (female).
Nor is that the only distinction we roll right over in English. We do not, for example, distinguish between an uncle by blood (related to one of my parents) and an uncle by marriage (wed to the sibling of one of my parents) — but Persian does. Nor do we distinguish between an uncle on the maternal side and one on the paternal, but again, other cultures do. We don’t have a formal term to describe how my husband relates to my brother’s wife — are they in-laws? Ish? (In my family we sometimes jokingly call this an “out-law” relationship.) Or what about in a polygamous household? Are your father’s other wives or your mother’s other husbands also your mothers and fathers?
Or let’s take siblings. English makes only one distinction there, on the basis of gender. In some East Asian languages, though, seniority also plays a role, so that you have different words for an older brother (ani in Japanese; gēge in Mandarin) and a younger one (otōto; dìdi), an older sister (ane; jiějie) and a younger (imōto; mèimèi). Obviously it’s possible to note the difference in English, as I’ve just done here — but those aren’t standard kinship terms, the kind of thing you might find listed in a dictionary. They’re descriptive phrases, and read somewhat awkwardly if you have one character regularly address another as “Elder Sister.”
Then you have what we nowadays call a blended family, where the basic structure gets complicated by changes along the way. When you share one but not both parents with someone else, we call that person your half-sibling. When you share no blood relationship at all, but one of your parents has wed one of theirs, that person becomes your step-sibling, and the new spouse becomes your step-parent. Sometimes this gets extended to step-grandparents, step-uncles, and so forth. (Interestingly, though you might think the “step-” prefix indicates a degree of separation, in fact it seems to derive from an Old English word for “orphan.”)
One of the reasons kinship categorization matters so much is that it defines the boundaries of taboo and permissible behavior. “Consanguinity” is the term for how closely you’re related so someone, and in most places and times anything within the second degree — i.e. parents or grandparents, children or grandchildren, or siblings — is considered incest. Nowadays we also tend to think of first cousins as being too closely related, but that’s a relatively recent development; it used to be quite common in the West, and is still common in other parts of the world, for a first cousin to be an ideal match. But consanguinity is one of the grounds on which a Catholic marriage can be annulled; if you’re too closely related, your marriage is not just ended (a la divorce), but was never valid in the first place.
It isn’t always defined along purely genetic lines, though. As I noted last week, you may not be considered as closely related to your relatives on the matrilineal side if your society is patrilineal. For example, in East African Habesha Christianity, you can’t be connected to your spouse within seven generations on your father’s side, but on your mother’s, the limit is four. Whereas in societies where clans or other large lineage groups are exogamous (marrying out), anybody who belongs to that group is considered taboo for you to wed, regardless of how much (or how little) genetic material you actually share.
In spec fic, of course, there’s endless room to play with this. A society that has shed a lot of gendered trappings might speak only of parents, siblings, children, without bifurcating those into pairs of terms; Rich Burlew has done this with elven society in his webcomic The Order of the Stick. For a society where the nuances of familial relationship govern huge swaths of society, you might resurrect archaic phrasing like “sister-son” and “brother-son” to distinguish between two different nephews. Or you could invent kinship terms to get around the English-language clunkiness of constantly referring to characters as “Elder Brother” and “Younger Sister” — though if you’re going to do that, you need to use those terms early and often so the reader will internalize them properly. And even then, some people will bounce off that as an added hurdle.
But maybe not as many as in the past. As our society becomes more multicultural, we become more aware of these practices in other communities. I watched the Chinese drama Nirvana in Fire around the time that the younger of my half-Taiwanese nephews became verbal enough to call his older brother gēge, a term I’d learned from the show; it’s now entered my vocabulary and my consciousness in a way it hadn’t before. Even if you use a different word, your East Asian readers may feel a thrill of recognition rather than confusion when they read about your characters making such distinctions.