Stutter

I force you to Stutter.

Speak

This spell causes the target to be unable to speak except in a halting stuttering manner for the duration of the spell.

This renders them unable to cast any magic which requires verbals.

Note: At character creation, this spell must be chosen before any other spell of it's level can be added to your book. In instances where multiple spells like this are available, only one needs to be chosen.