[@pkken] Probably varies on a case-by-case basis. Since they're all derived from things Aura users did in the past prior to the development of Incantations, it probably depends on how well-known and how complex the "story" you're trying to invoke is. 

To compare it to a real-world example, if Incantations were a thing in our world, you could just say "Excalibur!" and voila, you've invoked the sharpness of perhaps the most well-known legendary sword in the world. You don't need to explain what it is or does in order for the spell to work and cleave through whatever you're swinging it at -- though "telling" some of that story anyway could make the spell even more powerful in exchange for a longer cast time. On the other hand, if you were invoking something really obscure, like, say, a rain of spears conjured up by the Valkyrie Kara in a half-lost poetic epic only fragments of which have survived, then there [i]would[/i] probably be some explanation necessary -- a few lines of chanting to sort of set the stage for what it is you're trying to do and direct the collective memory to what, specifically, you're trying to call upon.

Obviously, the history and mythology of this world as I've told it is extremely bare-bones, so I'd encourage people using incantations to go a little wild and come up with some heroes and stories of their own to flesh out their repertoires of combat spells. But obviously, there's also always the classics to fall back on. Statistically speaking, somebody somewhere has thrown a fireball around, so that sort of spell doesn't really need a big flowery justification.