Kinship terms in sociology: primary, secondary and tertiary relatives with examples

In sociology and anthropology classes, "kinship terms" usually covers two lessons. The first ranks relatives by the number of family links between you: primary relatives are the members of your own nuclear families (parents, siblings, spouse, children), secondary relatives are their primary relatives (grandparents, aunts and uncles, in-laws, nephews and nieces), and tertiary relatives sit one step further out (first cousins, great-grandparents, an aunt's husband). The second lesson sorts the words themselves: terms of address versus terms of reference, and descriptive versus classificatory terms.

Both lessons were set out side by side in one book, George Peter Murdock's Social Structure (1949), and both are easier with a shorthand. Kin types are written as letters read outward from the person doing the reckoning, called Ego: F father, M mother, B brother, Z sister, S son, D daughter, H husband, W wife. MB is mother's brother; WZD is wife's sister's daughter. The notation guide has the full set, including the letters for elder and younger.

Where the three orders come from

Murdock began with the nuclear family and a plain observation: nearly every adult belongs to two of them. The family of orientation is the one you were born and raised in (F, M, B, Z). The family of procreation is the one you start by marrying (H or W, S, D). He credited those two phrases to W. Lloyd Warner, and he took the words primary, secondary and tertiary from A. R. Radcliffe-Brown's 1941 paper "The Study of Kinship Systems".

The definitions build on each other:

• Primary relatives: everyone in Ego's two nuclear families.
• Secondary relatives: the primary relatives of Ego's primary relatives, leaving out Ego and anyone already primary.
• Tertiary relatives: the primary relatives of secondary relatives who are neither primary nor secondary to Ego.

Nothing stops the ladder there. Murdock mentioned quaternary relatives (a first cousin once removed is one) and quinary relatives (second cousins), then chose to lump everyone beyond the tertiary rung together as distant relatives.

A counting rule you can check by hand

Each step is one primary link, so a relative's order is the number of letters in the shortest kin-type string that reaches them. F has one letter: primary. MB has two: secondary. FZH has three: tertiary. FBSS, a first cousin once removed, has four, which is exactly Murdock's quaternary example.

The word "shortest" does real work. FW, father's wife, collapses to M when she is Ego's own mother, so FW counts as a separate secondary relative only when she is someone else: a stepmother. FS is likewise a half brother only when he is not Ego's full brother.

Murdock counted 33 kinds of secondary relative and printed the list. Grouping his list by the primary relative each one runs through shows where 33 comes from.

7 + 7 + 3 + 3 + 7 + 3 + 3 = 33

Siblings and children add only three each, because their parents and siblings are already Ego's primary relatives. A brother's father is Ego's father; only the brother's wife and children are new. The spouse row is one row because Murdock treated WF and HF as one kind, and so on, whichever spouse Ego has. The list also contains stepparents, half siblings and co-spouses (a co-wife or co-husband), because Murdock was writing about the full range of marriage arrangements recorded across 250 societies, not only about the American household of his day.

Tertiary relatives multiply faster. Murdock put them at 151 kinds, among them the eight great-grandparents and the eight kinds of first cousin. That growth was his central point: no language could afford a separate word for every category, so every language groups relatives under shared terms.

One more pattern is worth noticing. For relatives linked only by descent, the order tracks average genetic sharing, and Murdock said as much: one half for primary relatives, about a quarter for secondary, about an eighth for tertiary. A half sibling, r = (1/2)^2 = 1/4, fits the secondary row; a first cousin, r = 2 × (1/2)^4 = 1/8, fits the tertiary one.

Kinship terms examples in a table

Here are familiar relatives placed by order, with the English word for each. "Consanguineal" means every link is a link of descent; "affinal" means at least one link is a marriage, which is how Murdock drew the line. The last two columns use his other classifications, explained below.

The word "uncle" appears twice, once for a secondary relative and once for a tertiary one. English ignores order entirely when it hands out that term.

Terms of address and terms of reference

Murdock's first way of classifying kin words is by how they are used. A term of address is what you say to a relative: "Mom, are you coming?" A term of reference is what you call that relative when talking about them to someone else: "my mother is coming."

In English the two sets overlap a great deal, and Murdock noted where they part. Nephew and niece are rarely used to address anyone. Terms for in-laws are seldom used in address at all; people use first names, or borrow a word for a blood relative and call a mother-in-law "Mom". The special address forms English does have are mostly familiar variants such as dad, grandpa, auntie and sis.

Reference terms tend to be the stricter set. "Mother" in reference normally means one woman, while "Mom" in address may stretch to a stepmother or a mother-in-law. Address terms can also be missing, for instance where custom forbids conversation with a particular in-law. For those reasons Murdock used only terms of reference in his comparisons. In between names and kin terms he noted teknonymy, the practice of calling a parent after a child, along the lines of "Maria's father".

If you are collecting terms yourself, ask the two questions separately. "What do you call her when you speak to her?" and "Who is she to you, when you mention her to a friend?" can get different answers from the same person.

Descriptive and classificatory: two meanings

Most exam confusion comes from this pair, because it has been used in two senses.

Lewis Henry Morgan, in Systems of Consanguinity and Affinity of the Human Family (1871), applied the words to whole systems. A descriptive system names collateral relatives by combining the basic terms: Gaelic (his "Erse") had no word for uncle and said "father's brother" or "mother's brother" instead. A classificatory system sorts relatives into broad classes and gives everyone in a class one term, so a father's brother can be called "father". Morgan filed the languages he called Aryan, Semitic and Uralian under the first heading and those he called Turanian, American Indian and Malayan under the second. Those family labels are long out of use, and Murdock rejected the old habit of treating the pair as a ranking of "primitive" against "civilized" peoples.

Murdock moved the words from systems to single terms and added a second scheme beside them. By range of application, a denotative term covers one kin type, such as father, wife or son-in-law, while a classificatory term covers two or more, such as grandfather, aunt, brother-in-law or cousin. On that test English is full of classificatory terms, and Murdock argued that almost every known terminology is classificatory, the exceptions being a few African societies that use descriptive terms wholesale.

By linguistic structure, a term is elementary if it cannot be split into parts with kin meanings (father, nephew), derivative if it adds a non-kin element to an elementary term (grandfather, sister-in-law, stepson), and descriptive if it joins two or more elementary terms. Murdock's example is Swedish farbror, father's brother, alongside which Swedish has morbror for MB, faster for FZ and moster for MZ. English builds descriptive phrases on demand when it needs to be exact: "my wife's sister", not just "my sister-in-law".

Classificatory terms are where whole terminologies differ. In an Iroquois-type system F and FB share a term and so do M and MZ, which makes FB's children "brothers" and "sisters". The kinship terms chart shows how six classic systems label the same sixteen relatives, and the six kinship systems explainer gives the history behind the labels.

Mix-ups that cost marks

• Primary relative and first-degree relative are not the same. The National Cancer Institute's dictionary counts blood links: a first-degree relative is a parent, sibling or child, and second-degree relatives include grandparents, aunts and uncles, nieces and nephews, grandchildren and half siblings. A spouse is primary for Murdock but no relative at all in a medical family history, and the same goes for step and in-law relations.
• Order is not cousin degree. A first cousin is a tertiary relative and a second cousin a quinary one. The "first" in first cousin has nothing to do with "primary".
• A descriptive term is not a descriptive system. Farbror is a descriptive term; Morgan's "descriptive system" was a claim about a whole language.
• A kin type is not a kin term. MB is a position in a family; "uncle" is a word that covers four positions in English.
• The orders measure genealogical distance, not closeness or importance. Murdock's own argument was that societies single out some secondary and tertiary kin for special rights and duties through rules of descent, so a relative several rungs out can carry more duties than the ladder suggests.

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Sources and further reading

• Murdock, George Peter (1949). Social Structure. New York: Macmillan. Chapter 1 (the nuclear family) and chapter 6 (analysis of kinship). Scan: archive.org
• Radcliffe-Brown, A. R. (1941). The study of kinship systems. Journal of the Royal Anthropological Institute of Great Britain and Ireland 71(1/2). doi.org/10.2307/2844398
• Morgan, Lewis Henry (1871). Systems of Consanguinity and Affinity of the Human Family. Smithsonian Contributions to Knowledge 17. Washington: Smithsonian Institution. Scan: archive.org
• National Cancer Institute. Dictionary of Cancer Terms: "first-degree relative" and "second-degree relative". cancer.gov