English "his", "her" and "their" are famously ambiguous. Jón took his book — whose book? It could be Jón's own book, or some other man's book; English leaves you to guess. Icelandic refuses to leave it open. It has a special possessive, sinn / sín / sitt, that means "his/her/their own" and can only point back to the subject of the clause. When the possessor is somebody else, Icelandic switches to the ordinary genitive pronouns hans / hennar / þeirra. The result is that an Icelandic sentence which an English speaker would render the same way can mean two completely different things depending on which possessive is chosen. Getting sinn right is not a nicety — it changes who owns what. (This page is about the reflexive possessive. The plain reflexive pronoun sig "himself/herself" — the object form — is a separate topic with its own page, as is the formal binding theory behind both.)
The core contrast in one minimal pair
Start with the sentence that defines everything. Take "Jón took his book":
Jón tók bókina sína.
Jón took his (own) book. (sína = reflexive → the book belongs to Jón, the subject)
Jón tók bókina hans.
Jón took his book. (hans = non-reflexive → the book belongs to some other man, NOT Jón)
Same English, two different Icelandic sentences, two different owners. sína (a form of sinn) is reflexive: it corefers with the subject Jón, so the book is Jón's. hans is the ordinary genitive of hann "he": it points at some other male already in the discourse, so the book belongs to a different man. There is no overlap. If you say bókina hans about a book that is in fact Jón's own, you have told your listener it is somebody else's — a real change of meaning, not a stylistic slip.
This is the whole engine of the system: subject's own → sinn; somebody else's → hans / hennar / þeirra.
Two kinds of agreement at once
sinn is doing two jobs simultaneously, and keeping them apart is the key to using it. It agrees in gender, number and case with the possessed noun (the thing owned), exactly like the possessive minn "my". But it corefers with the subject of the clause (the owner). These are independent.
So the gender of sinn tells you nothing about the owner's gender. In Anna las bókina sína "Anna read her own book", sína is feminine not because Anna is a woman, but because bók "book" is a feminine noun. The owner-link to Anna is fixed by the reflexive rule, regardless of sinn's ending.
sinn declines just like the possessive minn / mín / mitt:
| Masc. | Fem. | Neut. | Plural (m / f / n) | |
|---|---|---|---|---|
| Nom. | sinn | sín | sitt | sínir / sínar / sín |
| Acc. | sinn | sína | sitt | sína / sínar / sín |
| Dat. | sínum | sinni | sínu | sínum / sínum / sínum |
| Gen. | síns | sinnar | síns | sinna / sinna / sinna |
Watch the doubled consonants the orthography demands: masculine nominative/accusative sinn (double n), feminine dative sinni and genitive sinnar (double n), genitive plural sinna (double n) — while the forms with the long vowel keep a single consonant: sín, sína, sínum, sínu, síns (with the accent on í). The pattern is identical to minn, so if you know minn, you know sinn.
Hún elskar börnin sín.
She loves her (own) children. (neuter plural sín, agreeing with börn 'children'; coreferring with hún)
Hann sér ekki af bílnum sínum.
He won't part with his (own) car. (dative sínum, agreeing with masculine bíl)
Þeir seldu húsin sín og fluttu til Akureyrar.
They sold their (own) houses and moved to Akureyri. (neuter plural sín; subject = þeir)
In every one of these the gender/case of sín(um/a) comes from the possessed noun, while the ownership snaps back to the subject. Train yourself to compute the two links separately.
The most consequential example: "he loves his wife"
The textbook sentence that makes the stakes vivid is "he loves his wife". In English it is ambiguous and nobody notices. In Icelandic the choice of possessive decides whether he is faithful or not:
Hann elskar konuna sína.
He loves his (own) wife. (sína → the wife is the subject's own — the unremarkable reading)
Hann elskar konuna hans.
He loves his wife — i.e. some other man's wife. (hans → not his own; this implies an affair)
konuna sína is "his own wife"; konuna hans is "his wife" where his is a different man — so the second sentence says he is in love with someone else's wife. An English speaker who defaults to hans (because it looks like a straightforward translation of "his") can accidentally accuse the subject of adultery. This is the clearest illustration that the sinn / hans choice is semantic, not cosmetic.
María hringdi í mömmu sína.
María called her (own) mother. (sína → her own mother)
María hringdi í mömmu hennar.
María called her mother — i.e. some other woman's mother. (hennar → not María's own)
Why English can't do this — and what that means for you
English has exactly one set of third-person possessives (his, her, their) and uses it for both "the subject's own" and "someone else's". It has no reflexive possessive at all. Speakers fall back on context, or rephrase ("his own book") when they need to be explicit. Icelandic builds the distinction into the grammar: the moment a third-person possessive refers to the subject of its clause, the language requires sinn, and using hans / hennar / þeirra there is not just unusual — it actively asserts a different owner.
For the learner this means a habit has to be reversed. Coming from English, your instinct is to translate "his/her/their" with a single default word. You must instead stop and check the subject each time. If the possessor is the subject, the only correct choice is sinn; the genitive pronoun is wrong (or, worse, silently changes the meaning).
Strákurinn gleymdi töskunni sinni í skólanum.
The boy forgot his (own) bag at school. (subject = strákurinn → sinni, feminine dative with taska)
Ég hitti Jón og konuna hans.
I met Jón and his wife. (here the possessor 'his' is NOT the subject of the clause — the subject is ég — so hans is correct)
That last example is the important counter-case: sinn is only triggered when the possessor is the subject of the same clause. In Ég hitti Jón og konuna hans, the subject is ég "I", and "his" refers to Jón, who is not the subject — so the non-reflexive hans is exactly right. sinn is not "for the nearest noun"; it is specifically for the subject.
Common Mistakes
❌ Jón tók bókina hans.
If you mean Jón's own book, this is wrong — hans says it's another man's book.
✅ Jón tók bókina sína.
Jón took his (own) book.
The default English-to-Icelandic instinct — translate "his" as hans — flips the meaning when the owner is the subject. For the subject's own possession you must use the reflexive sína.
❌ Hann elskar konuna hans.
If he loves his OWN wife, this is wrong — hans implies another man's wife (an affair).
✅ Hann elskar konuna sína.
He loves his (own) wife.
This is the high-stakes version of the same error: hans where the possessor is the subject doesn't just sound odd, it asserts a different owner and changes who the wife belongs to.
❌ Hún las bókina sinn.
Incorrect agreement — bók is feminine accusative, so the form must be sína, not sinn.
✅ Hún las bókina sína.
She read her (own) book.
sinn agrees with the possessed noun, not the owner. bók is feminine, the object is accusative, so the form is sína. The owner being a woman is irrelevant to the ending.
❌ Ég hitti Jón og konuna sína.
Incorrect — the subject is ég 'I', not Jón; 'his wife' here must be hans.
✅ Ég hitti Jón og konuna hans.
I met Jón and his wife.
sinn is only triggered by the subject of the clause. Here the subject is ég; "his" refers to Jón (an object), so the non-reflexive hans is correct. Don't reach for sinn just because a male was mentioned.
❌ Þeir seldu húsin þeirra.
If they sold their OWN houses, this is wrong — þeirra implies other people's houses.
✅ Þeir seldu húsin sín.
They sold their (own) houses.
The plural works exactly like the singular: when the possessor is the plural subject, use the reflexive sín, not þeirra. þeirra would mean the houses belonged to some other group.
Key Takeaways
- sinn / sín / sitt is the reflexive possessive "his/her/their own": it can refer only to the subject of its clause.
- It agrees with the possessed noun (gender, number, case) but corefers with the subject — two independent links. The ending tells you about the thing owned, not the owner.
- When the possessor is not the subject (someone else, an object, a name in a list), use the non-reflexive genitives hans / hennar / þeirra.
- The choice is semantic: konuna sína "his own wife" vs konuna hans "another man's wife". Using the wrong one changes who owns what.
- sinn declines exactly like the possessive minn — same doubled-n / long-í pattern (sinn, sína, sínum, sinni, sinna).
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Start learning Icelandic→Related Topics
- The Reflexive: sig, sér, sínA2 — Icelandic's third-person reflexive pronoun — accusative sig, dative sér, genitive sín — which has no nominative, is invariant for gender and number, and is obligatory (and meaning-changing) whenever the object refers back to the subject.
- Possessive Pronouns: minn, þinn, sinn and hans/hennarA2 — Icelandic's split possessive system — the agreeing, postposed possessives minn, þinn and sinn that decline like adjectives, versus the frozen genitives hans, hennar, þeirra, okkar, ykkar that never change.
- Possessive Placement and DefinitenessB2 — Where the possessive sits and what the noun does around it: the default post-nominal possessive keeps the suffixed article (bíllinn minn), the preposed possessive is emphatic and drops the article (mitt hús), and inalienable possession — body parts, kinship — drops the possessive altogether in favour of a dative experiencer plus a definite noun (Mér er illt í hausnum 'my head hurts'), a construction English never builds.
- Long-Distance Reflexives: the Famous sigC1 — The construction that made Icelandic central to syntactic theory: the reflexive sig / sér / sín can be bound NON-LOCALLY — by the subject of a higher clause, across one or more clause boundaries — provided the intervening clauses are SUBJUNCTIVE. An indicative complement blocks the long-distance link and leaves only the local reading. The subjunctive, Icelandic's other flagship feature, is the licenser; one generalisation ties the two together.
- Personal Pronouns: Full DeclensionA1 — The complete four-case declension of every Icelandic personal pronoun, the three-gender third-person plural, the neuter það as 'it' and dummy subject, and the dative-experiencer construction (mér finnst).
- Icelandic Pronouns: OverviewA1 — A map of the Icelandic pronoun system — personal pronouns decline for all four cases, a true reflexive sig/sér/sín, possessives that agree with the noun, the invariant relative sem, and the universal þú with no polite 'you'.