Combine the past subjunctive of hafa (hefði, hefðir, etc.) with specific verbs to express regret, missed opportunities, and unfulfilled obligations.
"Should Have": hefði átt að
To say someone should have done something, use the conjugated past subjunctive of hafa + átt að + the main verb in the infinitive.
"Could Have": hefði getað
To say someone could have done something, use the conjugated past subjunctive of hafa + getað + the main verb in the supine form (the same form used after hafa).
Negation
To form negatives ("should not have" or "could not have"), place ekki immediately after the conjugated form of hafa.
| The teachers should not have underestimated this mess, they could have prevented it. | Kennararnir hefðu ekki átt að vanmeta þetta klúður, þeir hefðu getað fyrirbyggt það. |
| The boys are careless, they should have been prepared for the storm. | Strákarnir eru kærulausir, þeir hefðu átt að vera viðbúnir óveðrinu. |
| This was reckless, we could have shown more foresight. | Þetta var glæfralegt, við hefðum getað sýnt meiri fyrirhyggju. |
Questions and "If" Clauses
Invert the subject and the conjugated verb (hafa) to ask questions:
| Could you have prevented this accident? | Hefðir þú getað fyrirbyggt þetta slys? |
These constructions also work perfectly as the consequence in an ef (if) sentence. Because of the V2 (verb-second) rule, if the ef clause comes first, the main clause must start immediately with the verb (hefði):
| If he had shown foresight, he could have prevented the accident. | Ef hann hefði sýnt fyrirhyggju, hefði hann getað fyrirbyggt slysið. |