Undersøge ("to investigate, to examine, to research") is the workhorse verb of inquiry — what a doctor does to a patient, the police to a crime, a scientist to a question, and you to the contents of a suspicious cupboard. It is built transparently from the prefix under- plus the verb søge ("to seek"), and it inherits søge's key irregularity: although it looks like a regular verb, its past is the mixed-weak -te form undersøgte (not undersøgede). That one vowel-and-consonant shift is the main grammatical hurdle; the rest of the page is about using the verb and its very common noun undersøgelse in the right contexts.
Principal parts
| Form | Danish | English |
|---|---|---|
| Infinitive | (at) undersøge | to investigate, to examine |
| Present | undersøger | investigate(s) |
| Past | undersøgte | investigated |
| Past participle | undersøgt | investigated |
| Imperative | undersøg! | investigate! |
Why undersøgte and not undersøgede
This is the single most common error, so it is worth dwelling on. Danish weak verbs split into two classes: the big -ede class (lave → lavede) and the smaller -te class (spise → spiste, købe → købte). The verb søge belongs to the -te class, and a stem ending in -g after a long vowel drops into -gte in the past: søge → søgte. Every prefixed form built on søge inherits this — undersøge → undersøgte, ansøge → ansøgte, opsøge → opsøgte.
Politiet undersøgte stedet grundigt, før de slap pressen ind.
The police examined the scene thoroughly before letting the press in.
Lægen undersøgte hende og fandt ingenting alvorligt.
The doctor examined her and found nothing serious.
undersøge en sag / en patient
Undersøge takes a plain direct object — the thing or person being examined. Common objects span the medical, legal, and scientific worlds.
Vi er nødt til at undersøge sagen nærmere, før vi konkluderer noget.
We need to look into the matter more closely before we conclude anything.
Forskerne undersøger, hvordan klimaet påvirker fuglenes trækruter.
The researchers are investigating how the climate affects the birds' migration routes.
Notice that undersøge can take a full clause as its object — undersøge, hvordan... / undersøge, om... ("investigate how / whether...") — which is how it most often appears in academic and journalistic prose.
Rapporten undersøger, om de nye regler overhovedet har haft nogen effekt.
The report examines whether the new rules have had any effect at all.
The noun: en undersøgelse
The noun en undersøgelse is extremely common and conveniently covers three English nouns at once: an investigation, an examination, and a survey/study. Context tells you which.
| Danish | English | Domain |
|---|---|---|
| en lægeundersøgelse | a medical examination, a check-up | medicine |
| en politiundersøgelse | a police investigation | law |
| en spørgeskemaundersøgelse | a questionnaire survey | research |
| en videnskabelig undersøgelse | a scientific study | academic |
Jeg skal til lægeundersøgelse på torsdag.
I've got a check-up at the doctor's on Thursday.
En ny undersøgelse viser, at danskerne sover dårligere end før.
A new study shows that Danes sleep worse than they used to. (academic / news)
These nouns are compounds: læge + undersøgelse, politi + undersøgelse. Danish writes them as one word — splitting them (læge undersøgelse) is a frequent and conspicuous error.
undersøge vs forske vs granske
Three verbs cluster around "research / examine," and the distinction is about scope and register.
| Verb | Core sense | Register / domain |
|---|---|---|
| undersøge | examine a specific thing / question | neutral, all-purpose; takes a direct object |
| forske | do research (as an activity / career) | academic; intransitive, takes forske i |
| granske | scrutinise minutely, pore over | (literary) / formal; close textual study |
The key grammatical difference: undersøge is transitive (undersøge noget), while forske is intransitive and needs the preposition i (forske i noget = "do research into something"). You cannot forske en sag; you forsker i it.
Hun forsker i tarmbakteriers betydning for immunforsvaret.
She does research into the role of gut bacteria in the immune system.
Historikeren granskede de gamle breve linje for linje.
The historian scrutinised the old letters line by line. (literary / formal)
Jeg undersøgte priserne, før jeg købte billetterne.
I looked into the prices before buying the tickets. (everyday)
Common collocations and fixed expressions
- undersøge en sag — to look into a matter
- undersøge en patient — to examine a patient
- undersøge nærmere — to look into more closely
- undersøge mulighederne — to explore the possibilities
- lade sig undersøge — to get oneself examined (medically)
Du burde lade dig undersøge, hvis smerterne bliver ved.
You should get yourself examined if the pain continues.
Common mistakes
❌ Lægen undersøgede patienten i går.
Wrong past — undersøge is mixed-weak (-te), so the past is undersøgte.
✅ Lægen undersøgte patienten i går.
The doctor examined the patient yesterday.
❌ Hun forsker tarmbakterier.
forske is intransitive — it needs the preposition i: forske i noget.
✅ Hun forsker i tarmbakterier.
She does research into gut bacteria.
❌ Jeg har undersøget alle mulighederne.
Wrong participle — the -te class gives undersøgt, not undersøget.
✅ Jeg har undersøgt alle mulighederne.
I've explored all the possibilities.
❌ Jeg skal til en læge undersøgelse.
Split compound — it's one word: lægeundersøgelse.
✅ Jeg skal til en lægeundersøgelse.
I've got a medical check-up.
❌ Politiet forsker sagen.
One doesn't forske a case; one undersøger it (or forsker i a topic).
✅ Politiet undersøger sagen.
The police are investigating the case.
Key takeaways
- undersøger / undersøgte / undersøgt — mixed-weak -te verb (like its base søge); perfect is har undersøgt.
- It is transitive: undersøge noget/nogen, and can take a hvordan/om-clause as object.
- The noun undersøgelse covers investigation, examination, and survey/study — and forms one-word compounds (lægeundersøgelse).
- Contrast forske i (do research, intransitive) and granske (scrutinise minutely, literary).
Now practice Danish
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Start learning Danish→Related Topics
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- Compounding in DepthB1 — How Danish builds solid compounds — the head-final structure, the linking morphemes -s- and -e- and when each appears, recursive stacking, and the right-to-left strategy for decoding monsters like kvindehåndboldlandshold.
- Weak Past: The -te ClassA2 — The second weak class of Danish verbs — past in -te, participle in -t — and how to tell it apart from the larger -ede class.
- OpdageA2 — Full reference for the verb opdage ('to discover / notice / realise') and how it differs from finde and bemærke.
- The Past Tense: An OverviewA1 — How the Danish simple past (datid) splits into weak -ede, weak -te, and strong (vowel-change) verbs — and why you must learn each verb's class.