
Originally Posted by
Darske
Could a summoner with enough skill and aether summon a full primal on their own?
This will be answered by the final quest in the summoner storyline.
Tristan attempts to make one last, gigantic summon, but the effort literally consumes him in an inferno of aether.
In short, a single summoner will never have enough aether to summon a full-fledged primal.

Originally Posted by
Darske
I'm a bit confused as to how one actually differs from a primal aside from scale. Do they have any sort of independant will? (I lean towards yes on this one, given the end of the quest event for Titan-egi.) Do they posess the capacity to temper an individual?
An egi, as Y'mhitra explains, is merely an "essence" of a primal. Think of them as the "larval" aspect of the primal's true form. Though, to be sure, the jury is still out on what the primal's "true" form actually is. Read this thread to find out more: Are primals really primals?
As for whether the egi have independent will, I think they have basic animal instincts. Animals all have distinct personalities of their own, as any owner of a pet cat or dog would tell you. And try making a cat to do as you say. I'm fairly sure you'd agree it has pretty strong willpower. 
What I think you're asking, rather, is whether the egi are self-aware, in the way "true" people are. On that point, I'm not too sure either, but they clearly don't speak to the summoner the way full-fledged primals do, so I'm inclined to think that the egi are not "self-aware".
In short, I'd say the egi have animal-level intelligence, in keeping with the fact that they are no more than a mere fraction of a primal's true form.