I've argued for some both on CF and elsewhere that I don't think "conservative" and "liberal" are particularly helpful theological terms.
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If these--liberal and conservative--are to be regarded as theological categories, what do they actually and really describe? Is the difference between a theological liberal and a theological conservative a matter of, say, biblical [in]errancy or is it over matters of ancient and established Christian dogma (the Trinity, the Incarnation, etc)? Because certainly there is a radical difference between someone who doesn't accept biblical inerrancy and someone who rejects the Gospel itself.
-CryptoLutheran
In my opinion, liberal theology came from two places:
* Application of critical methods that started in the Renaissance to Scripture
* A suspicion of the use of Greek metaphysics in theology, that arise from a general skepticism of abstracts as expressed by Kant.
There have been a number of different responses to those challenges, but they’ve shared common assessments of traditional theology.
* One approach takes criticism far enough to believe that we can’t know enough about the 1st Cent for Scripture to be useful in any specific way. This approach recreates Christianity on general principles such as love and justice. I associate this with Schliermacher.
* One approach attempts to use the results of critical study to found Christianity on Jesus’ teachings as understood by modern scholarship. I associate this with Ritschl, and more recently with the “historical Jesus” movement. This approach tends to focus on NT scholarship over traditional theology.
* One approach starts with traditional Protestant theology, and updates it where changes are needed because of new exegetical understandings. I would associate this with Barth.
Most real Christian thinkers combine at least some of each approach, but in different amounts. The result is quite a broad spectrum, enough so to lead people to say that there’s no such thing as a liberal theology. But I think there is, because they’re all responding to the same basic concerns, and the groups aren’t all that separate. I think there’s really one liberal theological community, with a few different wings.
How does this interact with orthodox / non-orthodox? Not much. That’s primarily a criterion used by non-liberals. The liberal perspective almost by definition doesn’t use traditional theology as a norm. It’s our heritage. It often sets the terms in which we operate and the kinds of questions we ask. It lets us see the consequences of various positions, so we can avoid going down blind alleys that have already been explored and rejected. But ultimately, we don’t ask whether things are orthodox or not. We ask whether they reflect Jesus and Paul accurately. We ask whether they embody what the Gospel demands.
Most strands of liberal theology share two features:
* A strong concept of the Church. Most of this theology seems to come from Reformation Protestantism, i.e. from strands that are committed to theology being an enterprise of the community, the Church.
* A commitment to the Trinity and the Incarnation. All major strands of liberal theology are trinitarian. That's kind of interesting, given the apparently radical basis of liberal theology.