A common tactic when debating a creationist is the deliberate use of ambiguous terms. One example that I found recently was on a blog called Darwin’s God by Cornelius Hunter . The problem started with a comment by Cornelius where he asks in response to someone else’s comment “So SETI is not science?” What followed was a convoluted discussion about natural and non-natural causes as it relates to Methodological Naturalism.

First of all, Methodological Naturalism refers to the method of scientific inquiry in which only natural phenomenon are studied. Anything considered to be supernatural is not within the domain of study for such a naturalist. Science is essentially built on this methodology. That isn’t to say that the supernatural doesn’t exist, only that it is beyond the reach of science if it does.

Cornelius’ argument is that, assuming that all science necessarily conforms to Methodological Naturalism, then SETI (the Search for Extra-Terrestrial Intelligence) cannot be considered a scientific endeavor. Here’s his reasoning: Only natural phenomenon are allowed in scientific research. SETI, by definition, is looking for signals that are not natural (that’s how they infer intelligence). Therefore SETI does not conform to Methodological Naturalism and is therefore not science.

At a glance that seems reasonable. The problem is that it relies on an ambiguity in the term “natural”. You see, there are at least two different ways to use the term natural. One can say something is natural rather than supernatural, e.g. a person is natural whereas an angel is supernatural. Or one can say that something is natural rather than artificial, e.g. sugar is natural whereas aspartame is artificial. I don’t think you would say that a clinical trial of aspartame is not scientific because aspartame is not natural. Methodological naturalism uses the term natural as opposed to supernatural. SETI uses the term natural as opposed to artificial.

In the movie Contact, the protagonist hears a series of pulses that enumerate the primes from 1 to 101. It’s not natural in the sense that there are no known laws of physics that give rise to such a series naturally (as a counter-example, pulsars are considered natural because the pulses are the result of known laws). It is considered to be natural in the sense that no supernatural beings are assumed to be the cause of such a series.

Now this, of course, is a somewhat blatant ambiguity. Not all ambiguous terms are so clear cut. The differences can be quite subtle at times. I’ve been in arguments where it wasn’t until much later that I realized why I was having such difficulty with the terms. Which is the point, really. I was kept off balance by the fact that one term was being used in two different ways, with no clear demarcation.

Against a good rhetorician you must always keep an eye out for such ambiguous terms. They can be deadly in a debate.