fyrir, eftir, við: High-Frequency Polysemous Prepositions

Some prepositions you can file under a single English word. fyrir, eftir, and við are not like that — each is a whole bundle of senses, and each one packs several into a single short word you will use dozens of times a day. The danger for English speakers is treating them as if they had one meaning and one case. They do not: fyrir swings between "for," "in front of," "before," and "ago"; eftir between "after," "along," and "by [an author]"; við between "at," "by," "against," and "with." This page maps the high-frequency senses and — just as importantly — the case each sense takes, because the case is part of the meaning. (This page is not about the abstract two-case theory; for that, see prepositions/two-case-motion-location. Here we go sense by sense.)

fyrir — the four-way workhorse

fyrir is the trickiest of the three because its case actually depends on which sense you mean.

fyrir as "for" (benefactive) — accusative

When fyrir means "for the benefit of" someone — a gift for you, doing something for a friend — it takes the accusative.

fyrir as "ago" — dative (and this one surprises everyone)

Here is the single most useful thing on this page. To say "X ago" — a week ago, three days ago, a long time ago — Icelandic uses fyrir + dative. The English word order ("a week ago") puts the time first; Icelandic puts fyrir first: fyrir viku ("a week ago"). And the noun is dative, not the benefactive accusative.

Get this contrast clear: gjöf fyrir þig ("a present for you," accusative) versus fyrir viku ("a week ago," dative). Same word fyrir, different sense, different case. The "ago" sense is so common that mastering fyrir + dative for it is one of the highest-value things on this page.

fyrir as "in front of" — dative (static)

In its spatial sense, "in front of," fyrir describes a static position and takes the dative. You will meet it in fixed expressions like standa fyrir ("stand in front of / represent") and fyrir framan ("in front of").

fyrir as "before" (time) — and the idiom layer

fyrir also appears in temporal "before" expressions and in a thick layer of idioms — fyrir hádegi ("before noon / in the morning"), fyrir löngu ("long ago"), passa fyrir and so on. The lesson is not to learn a single case for fyrir but to learn it sense by sense: benefactive "for" (acc.), "ago" (dat.), spatial "in front of" (dat.).

eftir — "after", "along", and authorship

eftir is friendlier because most of its senses take the same case, but it has one use English speakers rarely guess.

eftir as "after" (time) — accusative

The everyday meaning is "after" in time, and — this surprises learners who expect a "rest = dative" logic — it takes the accusative. This is your bread-and-butter eftir. (The trap is that the nouns below — kvöldmat, hádegi, vinnu — happen to have identical accusative and dative singular forms, so you can't see the case on them; but with a noun whose cases differ it shows up clearly: eftir matinn "after the meal," not eftir matnum.)

eftir as "by [an author / creator]" — the one to memorise

This is the sense that has no obvious English hook. To say a work is "by" someone — a book by an author, a song by a composer, a painting by an artist — Icelandic uses eftir. English "by" here makes learners reach for af or frá; the right word is eftir.

Keep this apart from the passive agent, which is af + dative (skrifuð af Halldóri — "written by Halldór"). When you name the creator of a work as a label — "a book by X," "a song by X" — it is eftir. (The two can coexist: bók eftir Halldór names the author; skrifuð af Halldóri describes the action of writing.)

eftir as "along" — dative

Here is the case split worth holding onto: temporal eftir ("after dinner") is accusative, but spatial eftir — "along" a road or path — takes the dative. The same little word marks the two senses with two different cases.

við — "at", "by", "against", "with"

við is everywhere, and its senses cluster around contact, proximity, and interaction. In its most common modern uses it takes the accusative, though you will see it described as two-case in older or more technical treatments; for B1 purposes, learn the high-frequency frames as chunks.

við for location / proximity — "at, by"

A workhorse frame is við hliðina á ("next to / beside," literally "at the side of"), which pairs við with á + dative:

við for interaction / contact — "with, against"

við also marks the party you interact, talk, or come into contact with — tala við ("talk to/with"), hitta við, rekast við — and the thing you lean or bump against.

Note that English "talk to" becomes tala við (literally "talk with/at"), and "talk about" is the separate tala um — so a single English sentence can need both: tala við þig um þetta ("talk to you about this").

Common Mistakes

Treating "ago" fyrir like the benefactive "for" fyrir. The "ago" sense takes the dative: fyrir viku.

Using af for "a book by X." Authorship is eftir; af is the passive agent ("written by").

Mixing up the cases of fyrir: benefactive "for" is accusative (þig), while "ago" is dative.

English "talk to" is not tala til — it is tala við (+ accusative).

Two errors at once: temporal eftir is accusative, not dative (the dative kvöldmatnum is wrong), and the idiomatic time phrase uses the bare noun anyway — eftir kvöldmat, eftir vinnu, eftir hádegi. Reserve dative eftir for the spatial "along" sense (eftir veginum).

Key Takeaways

• fyrir is sense-dependent in case: benefactive "for" → accusative (fyrir þig); "ago" → dative (fyrir viku); spatial "in front of" → dative. Learn it sense by sense, not as one word.
• "X ago" = fyrir + dative: fyrir viku, fyrir mörgum árum. This is the highest-value pattern here.
• eftir = "after" (time, + accusative: eftir kvöldmat, eftir matinn) and, crucially, "by [an author/creator]" (also accusative): bók eftir Halldór, lag eftir Björk — not af. The dative is reserved for spatial "along" (eftir veginum).
• The passive agent "written by" is the separate af
  • dative; authorship "a book by" is eftir. English "by" hides both.
• við clusters around contact/proximity/interaction: bíða við dyrnar ("wait by the door"), tala við þig ("talk to you"), við hliðina á ("next to"). "Talk to" is tala við, not tala til.