Does the penalty for not having a Martial Weapon
Proficiency feat stack with the penalty for not having an
Exotic Weapon Proficiency feat? For example, what
happens if a sorcerer uses a bastard sword in one hand and
does not have either the Martial Weapon Proficiency or the
Exotic Weapon Proficiency feat for a bastard sword? Is her
penalty a straight –4 for not having the Exotic Weapon
Proficiency, or does she suffer a –4 for not having the
Martial Weapon Proficiency in addition to the –4 for not
having the Exotic Weapon Proficiency because a bastard
sword requires special training to use with one hand?
No, you don’t get two penalties for nonproficiency. You’re
either proficient with a weapon or you’re not.
If you’re Medium-size, you have to be proficient with a
bastard sword to use it in one hand; if you’re not proficient, you
don’t have the option to use the sword one-handed at all.
Assuming that the sorcerer in your example is Medium-size,
she would have to use the sword in two hands and would suffer
the –4 nonproficiency penalty when doing so.