The Potential Indicative
The indicative is sometimes accompanied by the idea of contingency. This idea is given by the use of ἄν, the meaning of the verb, or by context. ἄν may or may not be used.
The indicative may be used to express a necessity and from the necessity an obligation. Usually with ἔδει.
Wish (unfulfilled- ὀφείλον – would that) or impulse.