Learn Hardcore Norwegian: Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok. - When I do not understand grammar, I look it up in a dictionary.

In Norwegian, ikke (not) normally comes after the verb in main clauses, but in subordinate clauses (clauses introduced by words like når, fordi, at etc.), the word order changes.

Your first part, "Når jeg ikke forstår grammatikk", is a subordinate clause introduced by Når (when). The typical word order inside such a clause is:

Subject – (adverbs like ikke) – Verb – (objects, etc.)

So:

jeg = subject
ikke = negation adverb
forstår = verb

Hence: "jeg ikke forstår" is the correct subordinate clause order. Saying "Når jeg forstår ikke grammatikk" would be wrong.

Why does the second clause say "slår jeg opp" and not "jeg slår opp"?

The second part, "slår jeg opp i en ordbok", is a main clause. In Norwegian main clauses there is a verb-second rule: the finite verb usually comes in second position.

When a main clause starts with something other than the subject (here, the first clause "Når jeg ikke forstår grammatikk" comes first), the verb of the main clause moves in front of the subject:

Clause order:

Entire first clause: Når jeg ikke forstår grammatikk,
Finite verb of second clause: slår
Subject of second clause: jeg
Rest: opp i en ordbok

So we get: "Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok."

If you started the sentence directly with the main clause, you could say:

Jeg slår opp i en ordbok når jeg ikke forstår grammatikk.

Here, jeg is first, so the verb (slår) is second: jeg slår opp …

What does "slår opp" mean here? It looks like “hit up” literally.

Literally, slå = hit, and opp = up, but together slå opp is a phrasal verb meaning:

“to look up” (information) in something like a dictionary, book, etc.

So:

slå opp i en ordbok = to look (something) up in a dictionary

Just like English phrasal verbs (look up, turn off), Norwegian often separates the verb and the particle in main clauses:

Jeg slår opp ordet. = I look the word up.
Jeg skal slå opp ordet. = I will look up the word.

You almost always need opp with slå in this meaning; slå i en ordbok would not mean “look up”.

Why is there no article before "grammatikk"?

In Norwegian, abstract, uncountable nouns (like grammatikk, kjærlighet, musikk) are often used without an article when speaking in general:

Jeg liker musikk. = I like music.
Hun studerer historie. = She studies history.
Jeg forstår grammatikk. = I understand grammar.

If you say grammatikken, you’re talking about a specific grammar (e.g. the grammar of Norwegian, or the grammar in this book):

Jeg forstår ikke grammatikk. = I don’t understand grammar (in general).
Jeg forstår ikke grammatikken i denne boka. = I don’t understand the grammar in this book.

So dropping the article here is the natural, general statement.

Why is it "i en ordbok" and not "i ordboken", like “in the dictionary”?

Both are possible, but they differ slightly in nuance:

i en ordbok = in a dictionary (any dictionary; you just use some dictionary when needed)
i ordboken = in the dictionary (a specific one that both speaker and listener have in mind)

In everyday speech, i en ordbok is very natural if you mean “I look it up in a dictionary, in general, when this situation happens.” If you had previously mentioned a specific dictionary, you’d say i ordboken.

Why is it "en ordbok" and not "et ordbok"?

Norwegian nouns have grammatical gender. Ordbok (dictionary) is a common gender noun (formerly “masculine/feminine” group), so it takes the article:

en in indefinite singular: en ordbok
ordboken in definite singular: ordboken

If it were a neuter noun, it would take et: for example, et hus (a house). But ordbok is not neuter, so et ordbok is incorrect.

Could you use "Når" here to mean both “when” and “if”?

Yes. Når can mean:

When (every time / whenever something happens):
- Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok.
  = Whenever I don’t understand grammar, I look it up in a dictionary.
In many contexts, it also overlaps with English “if” when you’re talking about a repeated or expected situation.

If you want to emphasize pure condition (closer to “if”) rather than “whenever/when”, you can also use hvis:

Hvis jeg ikke forstår grammatikk, slår jeg opp i en ordbok.

That also works and is very natural. Når tends to sound slightly more like a repeated or certain situation; hvis is more purely conditional.

What tense are "forstår" and "slår" in, and why is that used?

Both forstår (understand) and slår (hit/strike, here part of slår opp) are in the present tense.

Norwegian present tense is used for:

Actions happening now
Habits and general truths

Your sentence expresses a habitual action: what you normally do in that situation.

English does the same thing: “When I don’t understand grammar, I look it up in a dictionary.” Norwegian mirrors that with the simple present: forstår / slår.

Why is there a comma before "slår jeg opp i en ordbok"?

Norwegian normally uses a comma between:

a subordinate clause and
the main clause that follows it,

especially when the subordinate clause comes first.

So:

Når jeg ikke forstår grammatikk, = subordinate clause
slår jeg opp i en ordbok. = main clause

You put a comma between them:
Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok.

If you reverse the order, you usually don’t put a comma:

Jeg slår opp i en ordbok når jeg ikke forstår grammatikk.

Can I move "ikke" somewhere else, like in English “When I do not understand grammar”?

Norwegian word order is stricter than English. The default in a subordinate clause is:

Subject – (adverbs like ikke) – Verb

So the natural order is:

Når jeg ikke forstår grammatikk …

These alternatives are wrong or very unnatural:

✗ Når jeg forstår ikke grammatikk
✗ Når ikke jeg forstår grammatikk (very marked, and basically not used in normal speech)

In a main clause, however, the verb typically comes second, and ikke comes after that verb:

Jeg forstår ikke grammatikk. = I don’t understand grammar.
Forstår du ikke grammatikk? = Don’t you understand grammar?

Could I drop "jeg" like in Spanish or Italian, and just say "Når ikke forstår grammatikk, slår opp i en ordbok"?

No. Norwegian is not a “pro‑drop” language. You almost always need an explicit subject pronoun like jeg, du, han, hun.

So you must say:

Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok.

Dropping jeg (Når ikke forstår grammatikk, slår opp …) is ungrammatical in standard Norwegian.

Is there any difference in meaning between "Når jeg ikke forstår grammatikk, slår jeg opp i en ordbok." and "Når jeg ikke forstår grammatikk, så slår jeg opp i en ordbok."?

You can add så in the main clause:

Når jeg ikke forstår grammatikk, så slår jeg opp i en ordbok.

This is very common in spoken Norwegian. The meaning is essentially the same. Så here works a bit like an extra connector: “then”.

The version without så is slightly more neutral and often preferred in more formal writing, but both are correct and natural.