Strong Masculine: -ir Plural (gestur type)

Icelandic strong masculines split into two big plural camps, and the split is the single most error-prone thing about masculine nouns. One camp — the hestur type — takes -ar in the nominative plural (hestur → hestar). The other, covered here, takes -ir: gestur ("guest") → gestir, staður ("place") → staðir, vinur ("friend") → vinir. The cruelty of the system is that the two camps are identical in the singular — same -ur nominative, same -s or -ar genitive — so nothing inside a singular sentence tells you which plural is coming. The only reliable signal is the citation (dictionary) form of the word, which you simply have to know. And because many of the highest-frequency masculines in the language sit in this -ir camp, the lazy heuristic "when in doubt it's -ar" fails on exactly the words you use most.

The defining endings: gen.sg -s, nom.pl -ir

This subclass is defined by a specific endings profile. In the singular it behaves like an ordinary strong masculine; in the plural it switches to the -ir / -i / -um / -a set. Here is the model noun gestur ("guest") in full — the cleanest member of the class, with no umlaut to distract you:

The four plural endings to lock in are -ir / -i / -um / -a. Compare them against the hestur type, which runs -ar / -a / -um / -a: the difference lives entirely in the nominative plural (-ir vs -ar) and the accusative plural (-i vs -a). The dative plural (-um) and genitive plural (-a) are the same in both camps. So when you misclassify a noun, the damage shows up precisely in the form you reach for most — "the guests arrived," a nominative plural.

staður: the -ir type that also umlauts

Most of the difficulty in this class comes from members whose stem vowel is a, because that a triggers the u-umlaut: wherever an ending contains (or historically contained) a u, the stem a rounds to ö. In a -ir masculine, the only ending with a u is the dative plural -um — so the umlaut surfaces in exactly one cell. Watch staður ("place, spot"):

Two things to flag. First, the dative plural is stöðum, not *staðum — the a rounds to ö before the -um. This is the same sound law that turns land → löndum and barn → börnum; it is fully predictable and you should expect it on every a-stem masculine. Second, note the genitive singular -ar (staðar), not -s. Both -s and -ar genitive-singular endings occur in this subclass, and the choice is lexical — gests but staðar. The plural type (-ir) does not tell you the genitive singular, so you learn the two singular pieces (acc.sg and gen.sg) as part of the word.

vinur vs staður: not every member umlauts

It is tempting to assume every -ir masculine umlauts in the dative plural, but the umlaut only happens when the stem vowel is a. A member like vinur ("friend") has i in the stem, so there is nothing to round — its plural is plain vinir / vini / vinum / vina, with vinum, not any umlauted form. Lining the two up side by side makes the conditioning visible:

So the rule is mechanical: the -ir ending is shared, but the umlaut is conditioned by the stem vowel. Staður rounds because it has a; vinur does not because it has i. Always check the citation form's vowel — that is what tells you whether to expect an ö in the dative plural.

The irregular bær

A small number of -ir masculines have a stem ending in a vowel or a j, and bær ("town, farm") is the one you meet first — it is in every place name (Akurey­ri, Hafnarfjörður… and bær itself as a common noun). It inserts a -j- before vocalic endings, giving a paradigm that looks irregular but is perfectly regular once you see the j:

The æ is the same throughout (no umlaut — æ is not an a), but watch the -j-: it appears in bæjum (dat.pl), bæjar (gen.sg) and bæja (gen.pl), and is absent in bæir / bæi where the ending already begins with -i-. The nominative plural is still the class-defining -ir, just attached to the æ-stem: bæir.

Why the citation form is your only clue

Here is the structural reason this subclass is hard for English speakers. English plurals are almost entirely predictable from the singular: see guest, produce guests; see place, produce places. Icelandic refuses you that. The singulars of gestur (-ir type) and hestur (-ar type) are letter-for-letter parallel — gestur/gest/gesti/gests against hestur/hest/hesti/hests — yet the plurals diverge: gestir but hestar. No phonological rule predicts the split; it is inherited lexical class membership. So the practical discipline is: learn the plural with the word, the way you learn gender with the word. When you meet a new masculine, note its nominative plural in your memory as part of its identity — "hlutur, plural hlutir" — because you will never be able to reconstruct it later.

A short starter set of common -ir masculines worth memorising as a block: vinur → vinir (friend), gestur → gestir (guest), staður → staðir (place), hlutur → hlutir (thing/object), bær → bæir (town), réttur → réttir (dish/right), bekkur → bekkir (bench/class). Notice that réttur and bekkur both have stem vowels other than a, so they take no umlaut, whereas any a-stem in the group will round to ö in the dative plural.

Common Mistakes

Key Takeaways

• This subclass takes the plural endings -ir / -i / -um / -a, differing from the hestur type only in the nominative plural (-ir vs -ar) and accusative plural (-i vs -a).
• The singulars are identical to the -ar type, so the only reliable clue is the citation form — learn the plural with the word.
• a-stem members umlaut in the dative plural only: staður → stöðum. Non-a stems (vinur, gestur, hlutur) do not umlaut.
• Genitive singular is lexical: gests (-s) but staðar (-ar). The plural type does not predict it.
• bær inserts a -j- before vocalic endings (bæjum, bæjar, bæja) but still takes the class -ir plural: bæir.
• Beware "when in doubt, it's -ar" — the -ir camp holds many of your most frequent masculines (vinur, gestur, staður, hlutur, bær).