dürften
Dürften is the Konjunktiv II (subjunctive II) form of the verb dürfen, which means "to be allowed to" or "may." It is used to express hypothetical permission, polite requests, conditional mood, and probability in indirect or reported speech. It is not the simple past tense; the Präteritum (historical past) of dürfen is durften.
In its Konjunktiv II present, dürften takes the forms: ich dürfte, du dürftest, er dürfte, wir dürften,
Probability and indirect speech
Dürften is also used to express probability or likelihood in present contexts, especially with plural subjects:
The Präteritum form of dürfen is durften (ich durfte, du durftest, er durfte, wir durften, ihr durftet,
Dürfen as the base verb and its use as a modal auxiliary; contrast with können (ability) and