I-shift

Introduction

The I-shift is a phonological process (sound change) that appears in the following types of words in Icelandic:

• Irregular plurals of nouns, such as bók – bækur, þáttur – þættir;
• Comparative and superlative forms of certain adjectives, such as langur – lengri – lengstur;
• Present tense of strong verbs, e.g. bjóða – býð, taka – tek;
• Past subjunctive of strong verbs, e.g. væri, gæti, yrði.

It’s no longer an active process, which means that it only affects certain words. This is unlike the U-shift, which is wide-ranging and applied everywhere where the conditions for it exist.

Here we’ll also cover a vowel change known as fracture. This is technically not the I-shift, but affects words in a similar way and so it makes sense to learn it along with the I-shift.

Affected vowels

The I-shift affects the following vowels:

a o ö → e	ú jó jú → ý	á o ó → æ
u → y	au → ey	já → e é

These vowels are not affected by the I-shift:

é        i        í

Fracture affects the following vowels:

jö → i

Examples

Irregular noun forms

Masculine

There are a handful of strong masculine nouns ending in -ur that get an I-shift or fracture in the dative singular and in the nominative and accusative plural:

Vowel change	Nominative singular	Dative singular	Nominative plural
á → æ	dráttur máttur sláttur þáttur þráður	drætti mætti slætti þætti þræði	drættir mættir slættir þættir þræðir
jö → i	björn hjörtur kjölur Njörður	birni hirti kili Nirði	birnir hirtir kilir —
o → y	sonur	syni	synir
ö → e	börkur flötur hnöttur köttur 🐱 lögur mörður völlur vörður vöxtur þröstur örn 🦅 Hörður	berki fleti hnetti ketti legi merði velli verði vexti þresti erni Herði	berkir fletir hnettir kettir legir merðir vellir verðir vextir þrestir ernir —

Genitive forms

Nouns in this category that contain jö or ö in the stem will get reverse U-shift in the genitive singular and plural, e.g. nom. sing björn → gen. sing. bjarnar, gen. plu bjarna.

Feminine

Some strong feminine nouns get an I-shift in the nominative/accusative plural:

Vowel change	Nominative singular	Nominative/accusative plural
á → æ	tá	tær
ó → æ	bók bót fló kló könguló 🕷 ló nótt rót	bækur bætur flær klær köngulær lær nætur rætur
ú → ý	brú brún lús mús 🐭	brýr brýr lús mús
ö → e	önd 🦆 hönd 👋 rönd strönd	endur hendur röndur/randir strendur/strandir

Some notes:

• Nótt is bit strange, because in the plural it loses a t;
• When brún means augnabrún “eyebrow”, the plural is brýr. When brún means “edge, precipice”, the plural is regular: brúnir;
• Some nouns in the ö → e group also have a regular plural, e.g. rönd “stripe” → rendur or randir “stripes” (note that “regular” here means reverse U-shift 😉). In the case of strönd, the form strandir only appears in placenames like Hornstrandir.

-ur or -r?

If the word ends in the vowel that is affected by I-shift, the plural ending will be -r, e.g kló → klær. Otherwise, the plural ending will be -ur, e.g. bók → bækur.

The exceptions: lús “louse” and mús “mouse”, which simply become lýs “lice” and mýs “mice”.

Comparatives and superlatives

Some very common adjectives get the I-shift in their comparative or superlative form, e.g. stuttur – styttri – stystur. See Irregular comparatives and superlatives for a full list.

Present tense of strong verbs

The present tense of strong verbs is formed by applying I-shift to the vowel in the infinitive, e.g. fljúga → flýgur. See Present tense for examples.

Past subjunctive of strong verbs

The past subjunctive of strong verbs is formed by applying I-shift to the past tense third person plural, e.g. gátum → gæti. See Subjunctive for examples.