Questions & Answers about Undskyld, det var dumt af mig.
Why is dum spelled with a -t at the end here (dumt)?
The word dumt is the neuter form of the adjective dum (stupid). It gets a -t because it describes the pronoun det (that), which is a neuter word. Here, det refers to the general situation or the action that just happened.
Why do we use af instead of fra for 'of me'?
In Danish, when you comment on someone's behavior or character using adjectives like dum (stupid), sød (sweet), or pæn (nice), you use the preposition af. While fra generally means 'from' (like a physical location or sender), af is the correct preposition here, matching the English phrase 'stupid of me' perfectly.
Can I say jeg er ked af det instead of undskyld in this sentence?
You could, but undskyld is usually better for this specific situation. Undskyld is a direct apology for a mistake you just made. Jeg er ked af det often carries a slightly heavier emotional weight, meaning 'I am sad about it' or 'I deeply regret it', though it is also used for everyday apologies.
Is undskyld just a fixed expression, or does it come from a verb?
It is the imperative (command) form of the verb at undskylde, which means 'to excuse' or 'to apologize'. So literally, you are telling the other person 'Excuse [me]', but in everyday Danish it functions exactly like the quick English apology 'Sorry!'.