Breakdown of Du warst leichtsinnig. Du hättest mich warnen sollen.
sein
to be
du
you (informal singular)
haben
to have
mich
me
Questions & Answers about Du warst leichtsinnig. Du hättest mich warnen sollen.
Why does the sentence end with two infinitive verbs, warnen sollen?
This is the double infinitive rule. When you use a modal verb like sollen to form a past tense expressing what should have happened, you do not use a past participle like gewarnt. Instead, both the main verb (warnen) and the modal verb (sollen) stay in their infinitive forms at the very end of the sentence.
Why is it hättest instead of hast?
hättest is the Konjunktiv II form of haben. We use it here to talk about an unreal situation in the past, meaning something that should have happened, but did not. Saying Du hast mich warnen sollen would just state a past fact (You were supposed to warn me), whereas hättest expresses a reproach: You should have warned me, but you failed to do so.
What would happen to the word order if I made this a subordinate clause, for example by adding weil?
This reveals a very special exception in German word order! Normally, in a subordinate clause, the conjugated verb goes to the very end. But when you have a double infinitive, the conjugated verb (hättest) is placed right before the two infinitives, not after them. It becomes: ... weil du mich hättest warnen sollen.
Is there a good way to remember the vocabulary word leichtsinnig?