Charismatic philosophers are able to summon a Plot Element they have captured of their choice to the field of debate; this takes quite a bit of concentration, so it counts a standard action to summon the Plot Element. Plot Elements can have a wild variety of different effects.
If it's a living Element (e.g. an enemy or ally) then it usually appears for one turn, uses an attack or Ability, and then dismisses itself. If the element was willing when it was captured, or has been swayed to the Charismatic’s side, then the Charismatic is able to give it instructions to follow.
If it's an inanimate Element with some power, then effects may vary - the Element may stay on as long as the summoner wishes it to, or it may do its thing and dismiss itself right away.
The summoner may dismiss an Element on during his turn as a free action. Once an Element is dismissed, though, it will "fizzle" away and be unsummonable for a while - usually until the next fight or Challenge arises. The DM ultimately decides when a Plot Element can be resummoned.