Slå op

Slå op is one of the most productive phrasal verbs in Danish. The base verb slå means "hit, strike," but glued to the particle op it splits into four everyday senses that have nothing obvious to do with hitting: look something up, break up with someone, put up a notice, and open a book. This page nails the principal parts, then walks through each sense and the word-order rule that trips up English speakers.

Principal parts

Slå is a strong verb with an irregular past slog and participle slået. The particle op never changes.

The perfect uses har: har slået op. It is a transitive, activity verb in all its senses (you look something up, break up with someone, post a notice), so it never takes være. Mind the spelling of the participle: slået keeps the å and adds -et, giving the å-e-t sequence that learners often misspell.

Particle stress: the spoken signal

Slå op is a separable, stressed-particle verb: the stress falls on op, not on slå. This is how a listener knows you mean the phrasal verb and not the bare verb slå ("hit") followed by some other word. English does the same thing — compare the stress in "look it up" versus "look at it" — so the instinct transfers, but Danish enforces it strictly. Mispronouncing it with the stress on slå can make the phrasal meaning vanish.

Sense 1: look up (in a reference) — slå op i

Sense 2: break up (end a relationship) — slå op med

This is where slå op differs most from bare slå. Slå op med en kæreste means "break up with a partner" — no violence implied. The preposition is med.

Sense 3: put up / post (a notice) — slå et opslag op

Here the object is the thing you display. The related noun is et opslag ("a posting, a notice"), which you will recognize from social media — et opslag på Facebook is "a Facebook post."

Sense 4: open (a book) — slå op på

To "open a book to a page" is slå op på side ... — literally "strike open onto page ..." A teacher says this constantly.

Word order with objects and pronouns

The particle op is separable, and the placement of the object decides where it sits. With a full-noun object, you may put it before or after op, but Danish strongly prefers it after: slå ordet op and slå op i ordbogen both occur, yet slå ordet op is the default. With an unstressed pronoun object (det, den, ham), the pronoun is obligatorily placed before the particle: slå det op, never slå op det. This is the single most common error English speakers make, because English allows "look up it" to feel wrong but "look it up" to feel right — and Danish agrees, but enforces it as a hard rule.

English contrast: one English "look up," four Danish verb-particle ideas

English "look up" is a single phrasal verb that happens to cover dictionaries and websites. Danish slå op is broader and, crucially, not the verb you use for "look up to (admire)" someone — that is se op til ("look up to"). And "look something up" in the sense of finding a fact is slå op, but checking whether something is the case may instead be tjekke ("check"). Keep three apart:

The reason Danish reuses slå op for "look up" and "break up" is that both are opening/striking-open gestures: you strike a book open, and an old metaphor strikes a relationship open/apart. You do not need to feel the metaphor — just learn the two senses by the preposition: i (a reference) versus med (a partner).

Slå op vs the noun et opslag

Keep the verb and the noun apart. The action is slå op (two words); the result — a posting, a notice, a lookup entry — is et opslag (one word). Hun slog et opslag op literally pairs both: "she put a posting up."

Common Mistakes

Key Takeaways

• Principal parts: slå op – slår op – slog op – slået op; perfect always with har.
• Four senses: look up (i), break up (med), put up a notice, open a book (på).
• Stress the particle op; unstressed pronoun objects go before it: slå det op.
• The verb is slå op (two words); the resulting noun is et opslag (one word, neuter).