U-Shift in Unstressed Syllables

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by Siggi
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U-shift (AKA u-hljóðvarp, AKA A-víxl, AKA u-umlaut (not to be confused with the German ü which, confusingly, goes by the same name), AKA u-mutation), is a very common sound shift in Icelandic. An a that is followed by a u in the next syllable changes to an ö.

That sounds confusing, but then again, you already learned all this in the article on u-shift, didn’t you? If you didn’t, go read that first, because that article covered all the important basics that everyone should know. Here, we’re going to talk about more niche uses, or the u-shift in unstressed syllables.

In Icelandic, the first syllable of a word is nearly always stressed (emphasised), while the other syllables are generally unstressed.

In an unstressed syllable, an a that is followed by a u in the next syllable usually changes to a u. Now that sounds confusing; let’s make it easier!

The u-shift is very common and systematic in Icelandic, but you see it in unstressed syllables especially often in the past tense of verbs and in adjectives, so we’ll pay special attention to those.

Rule of Thumb

Basically, it‘s like this:

in a stressed syllable, a before u changes to ö

a_u -> ö_u

in an unstressed syllable, a before u changes to u

_a_u-> _u_u


This is, of course, a generalisation. Exceptions exist, no rule is a 100%, buyer beware, etymology affects everything, yada yada…but it’s a damn good generalisation, so we’ll stick with it!


In the first person plural (we), verbs add an -um in the past tense (often with an extra consonant, like ðum or dum or tum, but it’s the u that matters now). að hugsa - við hugsuðum, for instance. If there is an a in the stem (like tala), this will trigger a u-shift.

  • að ætla - við ætluðum > to intend - we intended
  • að spila - við spiluðum > to play - we played
  • að nota - við notuðum > to use - we used
  • að vakna – við vöknuðum > to wake up – we woke up


Adjectives add an -um in the masculine dative, and in all genders in the dative plural. góður – góðum, for instance. If there is an a in the stem (lika svipaður), this triggers u-shift, of course. 

(If you’re confused as to why a and u can co-exist in svipaður, remember that you don’t get u-shift in the masculine nominative.)

  • svipaður - gleyma svipuðum strák > similar - forget a similar boy
  • grunaður - bjarga grunuðum manni > suspected - save a suspected man
  • lokaður - koma að lokuðum dyrum > closed - come to closed doors

Chained U-shift 

What if there are TWO a’s in a word, both stressed and unstressed? Well, the unstressed a turns into a u, like normal, which triggers u-shift on the stressed a, as well.

You can call this a u-shift chain or cascade, and it’s really not as hard as it sounds. Remember: your conscious brain is terrible at learning sound shifts, but your subconscious brain is phenomenal at it. Just check out some examples, read a lot of Icelandic, listen to a lot of Icelandic, and you’ll have it in no time.


There are two a’s in the word tala (speak): one stressed (the first one) and one unstressed (the second one). Let’s check it out in the past tense.

Let’s take a look at some more examples, because examples are amazing for learning sound shifts. 

  • Að tala – við töluðum > to talk – we talked
  • Að dansa – við dönsuðum > to dance – we danced
  • Að baka – við bökuðum > to bake – we baked
  • Að kalla – við kölluðum > to call – we called


Fatlaður (handicapped) has two a’s, one stressed and one unstressed. Let’s see what happens when the dative -um changes the unstressed a to a u.


Yay for examples! 

  • fatlaður - bregðast fötluðum manni > handicapped - fail a handicapped man
  • aldraður - aka öldruðum konum heim > aged - drive aged women home
  • slasaður - breyta slösuðu fólki > injured - change injured people


The u-shift is one of the most common sound shifts in the Icelandic language. Like sound shifts in general, it’s super hard for the conscious mind to keep track of, but the subconscious mind is amazing at it.

The best way to learn the u-shift is to look at a lot of examples; read a lot of Icelandic; listen to a lot of Icelandic; and notice when it happens. You’ll be using it yourself in no time!

in a stressed syllable, a before u changes to ö

a_u -> ö_u

in an unstressed syllable, a before u changes to u

_a_u-> _u_u
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