There is a popular, but altogether mistaken idea that scientific theories differ from theological (or philosophical) ones in that the former can be falsified but the latter cannot. The popularity of this idea can perhaps be traced to the enduring influence of Antony Flew’s parable of the invisible gardener. But it’s flatly wrong. But the way it is wrong may surprise you.
Let’s start by getting our definitions straight. A “theory” is an over-arching explanatory framework for a range of facts. For example, the forensic investigator seeks to develop a theory to account for all the aspects of a crime scene (the facts). Likewise, a scientist seeks to develop a theory to account for all the aspects of some natural phenomena.
In a similar manner, the theologian seeks to develop a theory to account for all the aspects of some theological phenomena. Some examples of theological theories are Anselm’s satisfaction theory of atonement, the Kenotic theory of the incarnation, and the transubstantiation theory of the Eucharist. (The range of data that these particular theological theories seek to explain include data from scripture, tradition, and personal and corporate experience.)
Whether the theory in question is in forensics, natural science, or theology, it is mistaken to think it is ever falsified, except perhaps in exceptional cases. Rather, what happens (or what almost always happens) is that some recalcitrant datum is identified. Assuming the datum is confirmed, the defender of the theory must make a choice: abandon the theory or modify the theory to accommodate the datum.
Imagine, by analogy, that you have an accident in a car. In almost all cases, the car can, in principle, be repaired. The simple question is this: how much are you willing to pay to repair the car? By analogy, the worse the accident, the more serious the recalcitrant data. Just as you need to consider how much you’re willing to pay to repair the car, so you need to consider just how much you’re willing to modify to save the theory. And just as there comes a point where a car is no longer worth repairing, so there comes a time when a theory is no longer worth saving. That time comes when it fails to do what it was originally proposed to do: that is, explain things.
To sum up, theories are regularly proposed in many fields (e.g. forensic science, natural science, theology) and a particular theory can in principle be modified interminably to accommodate ever more recalcitrant facts. But at some point, the theory is no longer worth “keeping on the road”. On that day, it is not falsified: rather, it is merely abandoned on the side of the road.