I should know the answer to this, but I've never played a magus with a deficient art before.
When calculating the lab total and casting scores for a spell where the a requisite art is deficient, is the relevant total halved? I'm thinking yes, but can't find a rule.
What about a spell that only has a casting requisite? My thought is the lab total is not, but that if you use the requisite to cast then the casting score is halved.
Can anyone point me at the rule on this, or is it just common sense?