Questions & Answers about Wir hätten nicht so leichtsinnig sein dürfen.
Why are there two infinitives (sein and dürfen) at the very end of the sentence?
This is the double infinitive rule for modal verbs in the past tense. When you form the past Konjunktiv II (to express a past regret) with a modal verb, you don't use a past participle. Instead, you use a form of haben (here, hätten) followed by the infinitive of the main action (sein) and the infinitive of the modal verb (dürfen).
The translation says 'should not have', so why does the sentence use dürfen instead of sollen?
You absolutely could say Wir hätten nicht so leichtsinnig sein sollen. However, using dürfen (to be allowed to) makes the statement slightly stronger. It implies that being so careless was completely unacceptable or crossed a line, essentially meaning 'we had no right to be so careless'. In English, we usually still translate this stronger feeling simply as 'should not have'.
How can I remember the vocabulary word leichtsinnig?
It helps to break it down into its core parts: leicht means 'light' or 'easy', and der Sinn means 'sense' or 'mind'. Adding the ending -ig turns it into an adjective. So, someone who is leichtsinnig is literally 'light-minded'—or in natural English, 'careless' or 'reckless'.
Why is nicht placed before so leichtsinnig instead of at the end of the sentence?