howlingwolf said:
... it seems odd that and evocation specialist, who manipulates energy, just can't seem to do it very long, where a conjurer can bring something into physical being for hours. It would seem that an evoker could create an energy force that surrounds him fully on all sides, and is very similar to shield (but in all directions vs one). It would obviously have lower AC bonuses since the force is not concentrated at the front and actively intercepting shots. Seems like a time measured in the 10 min a level range would also not be unreasonable.
Well, there has to be a clear distinction between the two types of specialist, so maybe we should assume that conjuration spells sacrifice something of their raw power in exchange for a longer duration.
Let's compare Shield (Evocation) with Mage Armour (Conjuration, Creation), using school descriptions from the SRD:
Conjuration
Conjurations bring manifestations of objects, creatures, or some form of energy to the character (summoning), actually transport creatures from another plane of existence to the character's plane (calling), heal (healing), or create such objects or effects on the spot (creation). Creatures the character conjures usually, but not always, obey the character's commands.
Creation: The spell manipulates matter to create an object or creature in the place the spellcaster designates (subject to the limits noted above for conjurations). If the spell has a duration other than instantaneous, magic holds the creation together, and when the spell ends or is dispelled, the conjured creature or object vanishes without a trace. If the spell has an instantaneous duration, the created object or creature is merely assembled through magic. It lasts indefinitely and does not depend on magic for its existence.
Evocation
Evocation spells manipulate energy or tap an unseen source of power to produce a desired end. In effect, they create something out of nothing. Many of these spells produce spectacular effects, and evocation spells can deal large amounts of damage.
So, evocation spells unleash force effects or destructive energies which are usually very potent, but shortlived.
Whereas a conjuration (creation) spell would actually bring a object or creature into being, and that object or creature is being held together by the magic of the spell. The object or creature might be clearly different to most natural ones (think Phantom Steed, or Evard's Black Tentacles), but it is still a real entity, composed of matter, whereas an evocation effect is mainly force/energy.
Therefore, conjuration spells tend to be less potent/destructive, but also more controlled, more versatile, and longer lived.
Not only does this kind of thinking clarify the distinction between the two schools, it also prevents specialists from circumventing restrictions that result from being barred from certain schools of magic (which after all is their only drawback compared to a normal wizard!)