skilja is a verb with two lives. Its most common, everyday meaning is "to understand" — ég skil "I understand / I get it" is one of the first full sentences you will use in real conversation. But the same verb also means "to separate, to part, to leave (something) behind", and from that second sense come the idioms skilja við "to divorce / part from" and skilja eftir "to leave behind." It is a weak j-verb with a -di past, and the good news is that one paradigm covers both meanings.
Conjugation
Class: weak j-verb (the -di preterite). Auxiliary: hafa — ég hef skilið "I have understood." The stem vowel is i, which does not trigger u-umlaut, so no ö appears. The j surfaces before endings beginning with -a or -u (skiljum, skilja, skilji); the d of the past assimilates so the past stem is skild-.
| Principal parts | |
|---|---|
| Infinitive | að skilja |
| 3sg present | skilur |
| 3sg past | skildi |
| Supine | skilið |
| Person | Present (nútíð) | Past (þátíð) |
|---|---|---|
| ég | skil | skildi |
| þú | skilur | skildir |
| hann / hún / það | skilur | skildi |
| við | skiljum | skildum |
| þið | skiljið | skilduð |
| þeir / þær / þau | skilja | skildu |
| Person | Present subjunctive | Past subjunctive |
|---|---|---|
| ég | skilji | skildi |
| þú | skiljir | skildir |
| hann / hún / það | skilji | skildi |
| við | skiljum | skildum |
| þið | skiljið | skilduð |
| þeir / þær / þau | skilji | skildu |
| Non-finite & imperative | |
|---|---|
| Imperative (þú) | skildu |
| Imperative (þið) | skiljið! |
| Supine | skilið |
| Past participle (m/f/n) | skilinn / skilin / skilið |
| Middle voice (miðmynd) | skiljast — "to be understood; to part" |
Sense 1: "to understand" (+ accusative)
This is the high-frequency meaning. The thing understood — a word, a sentence, a situation, a person — is a direct accusative object, or a whole clause. Ég skil þig "I understand you"; ég skil ekki spurninguna "I don't understand the question." On its own, ég skil works like English "I get it / I see."
Fyrirgefðu, ég skil ekki alveg hvað þú átt við.
Sorry, I don't quite understand what you mean.
Skilurðu íslensku?
Do you understand Icelandic?
Ég skildi ekki neitt í fyrirlestrinum.
I didn't understand anything in the lecture.
Sense 2: "to separate / part / leave behind"
The second sense is physical or relational separation — to put a distance between things or people. Two phrasal idioms carry most of the everyday load:
- skilja við — to part from / separate from / divorce. Hún skildi við manninn sinn "she divorced her husband." Used intransitively, þau skildu simply means "they got divorced / split up."
- skilja eftir — to leave (something) behind. Ég skildi símann eftir heima "I left the phone behind at home."
Þau skildu eftir tuttugu ára hjónaband.
They got divorced after a twenty-year marriage. (Here eftir is the preposition 'after' — not the particle in skilja eftir 'leave behind'.)
Hún skildi við kærastann sinn í fyrra.
She broke up with her boyfriend last year.
Ég skildi lyklana eftir í vinnunni.
I left the keys behind at work.
How can one verb mean both "understand" and "separate"?
The two senses feel unrelated in English, but they share a single ancient core: to take apart, to discern. To separate things physically is to set them apart; to understand is to mentally separate a tangle into its distinct parts — to tell one thing from another, to discern the structure of what you hear. English actually preserves the same metaphor in the word "discern" (Latin cernere "to sift, separate") and in "I can't make it out." So when you learn skilja, you are not memorising two random meanings glued to one form; you are learning one idea — parting things into their pieces — applied either to objects in the world or to ideas in your head. Holding that single image makes the verb much easier to retain, and it explains why the grammar differs: the "understand" sense takes a plain accusative object (the thing discerned), while the "separate" sense leans on directional particles (við, eftir, frá) that say what you are parting from.
This also clears up a frequent worry: how does a listener know which sense you mean? Context and the particle do the work. A bare skilja + accusative noun is almost always "understand"; skilja with við / eftir / frá is "part / leave." There is essentially no real-world ambiguity.
skiljast — the middle voice
The -st form skiljast has two related uses: "to be understood / come across" (þetta skilst ekki "this isn't clear / can't be understood"), and "to part (from each other)" (leiðir skiljast "ways part"). The set phrase mér skilst (að…) "I gather / I understand that…" is extremely common and takes a dative subject mér — a quirky-subject construction worth memorising whole.
Mér skilst að þú sért að flytja til Akureyrar.
I gather you're moving to Akureyri.
Hér skiljast leiðir okkar.
This is where our paths part.
Common Mistakes
❌ Ég skiljaði ekki spurninguna.
Incorrect — skilja is a j-verb with a -di past (skildi), not a regular -aði past
✅ Ég skildi ekki spurninguna.
I didn't understand the question.
❌ Skilurðu við mér?
Incorrect — 'understand me' takes the accusative (mig); 'skilja við' with the dative would mean 'part from'
✅ Skilurðu mig?
Do you understand me?
❌ Ég skili þetta núna.
Incorrect — the 1sg present is the bare stem skil, not 'skili'
✅ Ég skil þetta núna.
I understand this now.
❌ Ég gleymdi og skildi síminn eftir heima.
Incorrect — the thing left behind is an accusative object, so it's símann (def. acc.), not nominative síminn
✅ Ég gleymdi og skildi símann eftir heima.
I forgot and left the phone behind at home.
Key Takeaways
- skilja / skilur / skildi / skilið — a weak j-verb with a -di past; the i stem means no u-umlaut.
- Sense 1, "understand" (+ accusative): ég skil þig — the most frequent meaning; ég skil alone = "I get it."
- Sense 2, "separate/part": skilja við = part from / divorce; skilja eftir = leave behind (object in the accusative).
- Keep skilja (understand) apart from vita (know a fact) and kunna (know how).
- Middle skiljast: mér skilst að… "I gather that…" (dative subject); leiðir skiljast "paths part."
- Auxiliary is hafa: ég hef skilið.
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