Yes of course , but You simply can't do truely interesting stuff unless you know Quantum field theory and the gravitational force if you want to do string theory . You have to be comfortable with hand-waving not rigorously defining and proving every thing .
you're assuming everyone wants to do string theory.
Theoretical Physics? What is that?<br />
I'm sorry. I'll probably know someday, but for now, this goes beyond my freshman-in-highschool level education.
You could think of it this way....
Theoretical Physics is everything in physics if you take away the experiments.
The guy with the atom smasher is playing with toys...
the theory guy like Einstein, is playing with chalk and a blackboard.
what have you taken with math, and what have you taken with physics, and where would you like to go with 'more courses'?
some people get a Bachelors in one and then hop to the other for grad school and fill in the gaps for a few semesters..
and others take an extra year or two, and aim for a mathematical physics degree where it's pretty easy to shift to one or the other, depending where you wanna specialize.
Basically some people dont wanna do real analysis, and other people arent too keen on a lot of intermediate electromagnetism.
I like to say that if you get a physics degree and you take analysis and you take differential geometry, fairly early on, you can wander anywhere in both subjects.
When you have
a. vector calculus, and
b.a whole textbook on differential equations
most everything hard is pushed out of your way, and
c. with differential geometry,
you can tackle most any course.....
yeah, its possible. Go research, nothings stopping you. You dont even need an education, just an imagination, and a firm grip on reality at the same time ha.