Learn Hardcore Icelandic: Við komum seint vegna mikillar umferðar.

Present: við komum = we come (e.g., habitually)
Past: við komum = we came/arrived Context decides which is meant. In a sentence like this, past is the most likely reading unless there’s clear habitual context.

Why is it seint and not sein(n)?

Seint is an adverb (“late”) modifying the verb komum (“arrive”). The adjective seinn/sein/seint describes nouns (“a late guest”), but with verbs you use the adverb:

Arrived late: Við komum seint.
Were late (describing us): Við vorum seinir (mixed/men) / Við vorum seinar (women).

What case does vegna take, and is that why it’s mikillar umferðar?

Vegna always governs the genitive. That’s why you see:

mikill (much/great) → feminine genitive singular mikillar
umferð (traffic, fem.) → genitive singular umferðar If you meant “because of the heavy traffic” (definite), you’d say vegna mikillar umferðarinnar.

Could I use út af instead of vegna?

Yes. Út af is common and a bit more colloquial; it takes the dative:

Við komum seint út af mikilli umferð. (dative: fem. sg. mikilli, noun umferð) Nuance: vegna is neutral/formal; út af is everyday speech. Both are fine here.

How would I say it with a full clause: “because there was heavy traffic”?

Use af því að to introduce a clause:

Við komum seint af því að það var mikil umferð. You’ll also hear vegna þess að það var mikil umferð (“because of the fact that…”), which is correct but a bit heavier in style.

Why not mikil umferð here?

You do say mikil umferð in a neutral subject sentence: Það var mikil umferð.
After vegna, you must use the genitive: vegna mikillar umferðar.

Can I move the cause to the front?

Yes, for emphasis or flow:

Vegna mikillar umferðar komum við seint. Icelandic allows such fronting of adverbial/prepositional phrases.

What’s the difference between “arrived late” and “were late” in Icelandic?

“Arrived late” (event of arrival): Við komum seint.
“Were late” (describing our timeliness): Við vorum seinir (men/mixed) / Við vorum seinar (women).
You can also express a resulting state: Við erum seint komnir/komnar (“we’ve arrived late,” focusing on the state of having arrived).

How do I choose between við and okkur?

Við is nominative (subject), so you need við komum.
The object forms are okkur (acc./dat.) and okkar (gen.). Example: Þau biðu eftir okkur (“They waited for us”).

Pronunciation tips for tricky bits?

Við: the ð is the “soft th” in “this.” Approx. “vith.”
komum: first vowel like “off,” second like “u” in “put.” Approx. “KOH-mum.”
seint: “saynt” (like English “saint”).
vegna: “VEGH-na” (the g is a soft, fricative “gh” sound).
umferðar: “UM-fer-thar” (the ð again like “this”).
mikillar: the “ll” is pronounced with a t-like flap: “MIK-it-lar.”

Can I use the perfect here?

Við höfum komið seint = We have come late (on some occasion(s); experience or recent past).
Við erum seint komnir/komnar = We have arrived late (resulting state).
For a single finished past event, simple past Við komum seint is most natural.

Is umferð countable? Could I say “many traffics”?

Umferð is uncountable in this sense. Use:

mikil umferð (“heavy/a lot of traffic”)
If you want to count things, switch to countable nouns:
margir bílar (“many cars”) → after vegna (gen. pl.): vegna margra bíla.

Where does the time expression go if I add one?

Common and clear:

Við komum seint í gær vegna mikillar umferðar. You can also front the cause: Vegna mikillar umferðar komum við seint í gær. Adverbs like seint usually follow the verb in simple statements.

How do I say “too late”?

Use of before the adverb:

of seint = too late
Stronger: allt of seint = way too late
Example: Við komum allt of seint vegna mikillar umferðar.

Why is it komum and not koma?

The verb agrees with the subject. With við (we), the present/past 1st person plural form is komum. Koma is the dictionary form and also the 3rd person plural present (e.g., þeir koma = they come).