Is minoring or majoring in theatre really different?
Oh yes. Minoring will barely be a vague overview of things, and it will almost never be performance based. It is also never something you need to audition for, as far as I know. Majoring is a very rigorous focus, often is audition based (my school accepted 1/100 students who auditioned) and will be a very in-depth look at whichever major you pick. I would say that minoring alone will not give you the training or understanding of the industry needed to work professionally, but it is a good way to spark your interest and look a bit deeper into theatre than you may have otherwise.
And it does make sense--minoring in theatre at my school was 7 classes, many of which filled requirements for other majors. Majoring was a full 5 classes a semester, at least, shows, tech hours... It was a lot.
