In their book Who Needs Theology?, professors Roger E. Olson and Stanley J. Grenz informally break theology up into five types, depending on how seriously it's applied and how accessible the thinking is. While not an "official" breakdown, it's useful to see the entire spectrum, since any two people may use different definitions as their own idea of "theology".
- Folk Theology is the most widespread and least "logical" kind. It advocates blind faith and and emotional spirituality, and tends to be very faddish, rejecting tradition and long-held truths in favor of whatever is popular. Folk theology doesn't just avoid analytical thinking, it resents it and considers it "unspiritual" or downright sinful. My own term for this is "armchair theology."
- Lay Theology is the theology of the layman. It involves critical thinking and logical study, but not necessarily beyond widely accessible books and texts. It seeks to answer spiritual questions using the actual religious documents and strives for internal consistency. It relies on an informal study of religious truth rather than a formal one and seeks to answer questions rather than reject them as showing a lack of faith.
- Ministerial Theology is the kind most people expect from community religious leaders and missionaries. It requires a formal study of theology, with a highly critical eye and a good knowledge of the background of the religious texts. Ministerial theology is thorough and practical, dedicated to answering the questions of the lay theologian. It is both broadly informed and highly relevant to others.
- Professional Theology is less oriented toward discipleship than ministerial theology, but is more informed about the specifics and nuances of spiritual questions common and rare. It's dedicated to formal study of source texts and a rigorous exploration of religious truth. It writes the books ministerial and lay theologians read, exploring their questions but leaving it to others to share them with the untrained believer.
- Academic Theology is the most intellectual and least accessible sort of theology. It's not intended for "common people", but for professional and other academic theologians. This is the kind most people use when constructing a negative image of theology: concerned with the fine details of religious history and truth, often extrapolating widely to connect different ideas. Just because it's not accessible doesn't mean it's not important, however. Academic theology works to ensure that religious teaching is consistent from the past through the present to the future.