Creo Mentem creates a strong inclination.
Rego Mentem forces someone to accept something as true; forces someone to perform a specific action; forces someone to enter a different state of consciousness (i.e. sleep or wakefulness).
We can step OC and look at it from a psychiatric perspective:
CrMe can create a philia or phobia of dogs- an emotional response to stimuli.
ReMe creates a compulsion, like with someone with Obsessive Compulsive disorder, who must perform an action but whose motivation isn`t emotional per se.
Or to think of it another way:
Creo creates something entirely new that was not there before.
-Create a new memory that had no natural cause (i.e. never happened)
-Create a new emotion that had no natural cause (i.e. Loyal to Cassen, Lust for Susanne, Hatred for Bob)
Rego forces something to move to new naturaly attainable locations.
Movements of the mind include
- Sleep to waking, and vice versa
- Functions of Logic -- from premise to conclusion.
- Functions of decision making -- the decision to act. You can force someone to do everything he can to protect Cassen, whatever emotions he might have about the issue.
- Changes of Pre-Existing emotions -- make someone who is already angry more or less angry, or keep the emotional state precisely as it is now, preventing new emotions from forming or existing ones from disappearing. This can be extreme: Change an emotion of disloyal to loyal (as its on a single characteristic scale.)
There are advantages for each.
CrMe spells are lower levels for similar effects.
However, CrMe can be overrriden by natural emotions or force of logic or freewill. They`re also easier to counter using other Mentem magics.
For example. You enchant Bob to be very loyal to you, a strong emotional bond. However, a clear thinking and dutybound man, Bob logically understands both that you are evil and must be destroyed, and that his emotions are not natural. Though he is filled with profound emotional pain and anguish for doing so, he kills you anyway. He cries uncontrolably until the spell wears off.
Or, you create and Bob`s mind the emotional urge to kill Jim. However, Jim counters by using ReMe, issuing a compulsion to not kill him, but you instead. He will obey the ReMe, because CrMe controls directly how he feels, but ReMe can control exactly what he does.
ReMe can make a disloyal person loyal; MuMe can turn Loyalty to Lust; CrMe can make them think of hotdogs.