Answer
There are, of course, many paths to teaching, especially in systematic theology. ST as a discipline really doesn't exist at secular universities and colleges. At Yale, there were courses called "systematic theology," but those were basically courses in modern theology from Schleiermacher to the present. You couldn't take a course there in ST in the traditional sense, namely studying what Scripture says on some subject or subjects. Since these schools reject biblical authority, they have also abandoned systematic theology.
You can get a doctorate in ST at a few evangelical schools: Westminster, Fuller, Trinity (I think), maybe some of the Scottish, Dutch, or South African universities. But it is good, if you want to teach ST, to get some experience with mainstream liberal thought, having gotten your basic biblical grounding at a place like RTS. So there are advantages to going to a secular university to do doctoral work, even though ST as such is not available there.
Now if you do go to a secular school for a doctorate, there are three possible subjects that will be useful in preparing you to teach ST: biblical studies, church history, and philosophy (or philosophical theology). Some noteworthy thinkers have come to ST by each of these routes: B. B. Warfield and Richard Gaffin from biblical studies, John Gerstner and many others through church history (see my essay, "Traditionalism" at www.thirdmill.org for some caveats), Van Til, Paul Helm, and others from a background in philosophy.
I came to the discipline by way of the philosophical theology program at Yale. My failure to finish the dissertation was my own failure, not theirs; they treated me well. I learned quite a bit, though I confess it was hard to be as serious about modern thought as they wanted me to be.
I guess I had always thought that after that study I might get a job teaching apologetics somewhere, but in God's providence the death of John Murray moved Westminster to look for another systematic theologian, and to my surprise Norman Shepherd, Murray's successor, contacted me at Yale (1967) about joining the WTS faculty. The rest is, if not history, at least public record, more or less.
If you enter the ST discipline by the philosophical route, you will be well-prepared to enter into arguments and debates. (I think church historians are much less able to do that.) But you will need to discipline yourself to become an exegete. Though I'm a philosopher by background, I agree with John Murray that exegesis is the heart of the systematic theologian's work. I was pretty well prepared to do that by my seminary studies at RTS, but I've sometimes wished I were even more fluent in Greek, Hebrew, and biblical hermeneutics.
Answer by Dr. John M. Frame
Dr. John M. Frame is Professor of Systematic Theology and Philosophy at Reformed Theological Seminary in Orlando, FL.