Questions & Answers about Vi hade inte låst dörren igår.
How do we form the past perfect ("had locked") in this sentence?
Just like in English, Swedish uses the past tense of "to have" (hade) followed by a special form of the main verb called the supine. Here, the supine of att låsa (to lock) is låst, so we get hade låst (had locked).
Why is inte placed between hade and låst?
In a standard Swedish main clause, a little word like inte (not) usually comes right after the first verb. Since hade is our first verb, inte goes immediately after it, splitting hade and låst.
Why does the supine form låst end in just a "-t"?
The verb att låsa belongs to a group of verbs whose stem ends in an unvoiced sound (here, an "s"). For this group (Group 2b), you form the supine by simply adding a -t to the stem, resulting in låst.
Can you break down the word dörren?
The base noun is en dörr (a door). To say "the door", we add the definite ending -en to the end of the word, creating dörren.