An invocation is an address to a god or muse to assist the epic poet in his composition. Milton invokes divine guidance at the opening of Paradise Lost:

'And chiefly Thou, O Spirit, that dost prefer

Before all temples th'upright heart and pure,

Instruct me..'

Literary epic was regarded by Renaissance critics as the highest of all genres. They share a series of features, derived ultimately from the epics of Homer. These include central figures of national or cosmic importance; ample settings; superhuman deeds in battle; active participation of divine beings in the action; and a grand and formal style. Epics also employ certain stylistic conventions: the poet begins by stating his argument or theme, invokes his Muse (in Milton's case the Holy Spirit) and poses his epic question which introduces the narrative proper:

'Say first what cause
Mov'd our Grand Parents in that happy State,
Favour'd of Heav'n so highly, to fall off
From their Creator, and transgress his Will
For one restraint, Lords of the World besides?'

The narrative also begins in medias res, at a critical point in the action. In Milton's case, the opening sees the fallen angels in hell, gathering their forces and determining their revenge.