Learn Danish: Hun må have planlagt udgravningen. - She must have planned the excavation.

In this context, må expresses a strong logical deduction (she "must have" done it), not an obligation. When you combine a present tense modal like må with a perfect infinitive like have planlagt, it expresses epistemic speculation—meaning you are making a confident guess about the past based on present evidence.

Why is "have" in the infinitive here instead of "har"?

Modal verbs like må are always followed by the infinitive form of the next verb. To speculate about a past event using a present-tense modal, we use the perfect infinitive structure. This consists of the infinitive have followed by the past participle planlagt.

Where does the "-lagt" ending in "planlagt" come from?

Planlagt is the past participle of the verb at planlægge (to plan). It is a compound of the noun plan and the verb at lægge (to lay or put). Because lægge is an irregular verb whose past participle is lagt, the compound verb follows the exact same irregular pattern.

How is the noun "udgravningen" constructed?

It is built from the verb at udgrave (to excavate), which consists of ud (out) and grave (to dig). The suffix -ning turns this verb into the noun udgravning (excavation), and the -en at the end is the definite article, making it udgravningen (the excavation).