This question is, of course, way too large to address in only one post. However, I was reading Berkhof’s Introduction to Systematic Theology (which is included in the Eerdman’s edition of his Systematic Theology), and I found a really fascinating discussion of this question that was eminently clear and precise. So, what I want to do here is to set forth Berkhof’s arguments and see what people think.
The question revolves around the definitions of the two terms. What one means by “theology” and what one means by “science” will carry the day in answering the question. It seems fairly obvious that if theology is a science, it is a science that is different from the “normal” sciences we think of today (e.g., physics, chemistry, biology, etc.). With the advent of Kant’s denial that human beings can truly know anything beyond what the senses can apprehend (Kant did not deny the existence of things beyond the realm of the phenomenal world; rather, he posited that they were objects of faith, not knowledge), theology as a science has fallen on hard times.
Berkhof makes the point that many people wanted to retain the idea that theology is a science, but they wanted to do so while being persuaded of Kant’s position. This meant that they had to make theology into a science of observable things (see p. 46). What is observable is the human psyche. So theology had to be redefined as the science of religion (as opposed to the majority definition in church history of theology being the ectypal (creaturely) knowledge of God). In other words, it became the science of what we can observe happening in human beings when confronted with the supernatural. It was thought that the supernatural itself could not be the object of scientific study, but our reaction to the supernatural could be observed.
Berkhof notes several problems with this train of thought. Firstly, this is too narrow a definition of science. If science is limited exclusively to the realm of what we can observe with our senses, then what of those branches of science that deal with the philosophy of science? The material they work with is not sensory information, but is dependent on rational intuition (pp. 46-47).
A second problem Berkhof raises is that science, like theology, is also dependent on revelation. Without a revealed world, science would have nothing to study. As hard as science often tries to get away from revelation, it cannot escape natural revelation at all.
A third problem is that the physical sciences and theology both have tests that can be performed. The physical sciences use the laboratory, whereas theology uses Scripture as a test.
Now, Berkhof asserts that theology is not a science in the same way that the natural sciences are. Theology has a different method, a method determined by the subject matter. However, the question may be raised as to whether science can be reduced to the scientific method. Remember the original meaning of the Latin scientia, which means “knowledge.” Most scientists today would deny that anyone can know God as an object of knowledge. They would typically say that one can only believe in God. However, such a position completely ignores the possibility of the Bible being revelation from God to us. We can know God through His revelation of Himself. That we believe the Bible is God’s revelation does not mean that theology is still all a matter of belief and not of knowledge. The scientist himself has to believe that the tools of his trade are trustworthy (his senses, and his reason). Does that make his field less an object of knowledge and only a matter of belief? Then neither does belief in the Bible as God’s revelation mean that theology is all reducible to belief and has no component of knowledge in it. In short, theology, when rightly defined, is a science, when science is understood in the above way.