As discussed in the previous essays on this subject, conspiracy theorists often use the methods of critical thinking to support and defend their theories. One method, which is a core component of scientific reasoning, is the inference to the best explanation. As the name suggests, this reasoning aims at finding the best explanation and this typically involves pitting competing explanations against each other until the best emerges.

This reasoning can be seen as a version of the argument by elimination. This argument has two basic forms. One version is the extermination method in which the goal is to show that something cannot be the case. The idea is to present all possible options, refute all of them and then conclude a total elimination. As an example, Kant used this method to argue that the existence of God cannot be proven (and that it could not be disproven). His reasoning was as follows:

Premise 1: There are only three possible ways to prove the existence of God: the teleological argument, the ontological argument and the cosmological argument.

Premise 2: None of these arguments can succeed in proving the existence of God.

Conclusion: There is no way to prove the existence of God.

While this is a valid deductive argument (if all the premises are true, then the conclusion must be true), showing that it is also sound (valid plus all true premises) is the real challenge. Doing so requires showing that there are only three ways to prove God’s existence and that they all must fail.

Since this method aims at total elimination, it is only useful in this context when trying to argue that no explanation is possible.

The second version is like a marathon: the competition runs until one victor emerges from the pack. In its simplest form (which has but two options), it can be presented as a disjunctive syllogism:

Premise 1:  P or Q

Premise 2: Not Q

Conclusion: P

It can also be expanded to include potentially infinite options:

Premise 1: P or Q or R or …

Premise 2: Not Q and Not R and Not…

Conclusion: P

This sort of reasoning is often used in mystery/crime stories: if there are only five possible suspects and one of them did it, then elimination four of them will reveal the culprit.  This presentation can be misleading, however. While the logic is valid, to avoid committing the fallacy of false dilemma it must be the case that the two (or more) options that are presented are the only viable options. To the degree that other options remain a possibility, the truth of the first premises remains in doubt.

Conspiracy theorists (and many others) sometimes make the mistake of falling into a false dilemma when they claim that their refutation of their main competitor(s) proves their theory. For example, a flat-earther might reason like this:

Premise 1: The earth is flat or the earth is a sphere.

Premise 2: The earth is not a sphere.

Conclusion: The earth is flat.

The obvious problem is that while the best-known earth shapes are spherical and flat, this does not entail that those are the only options. There are, after all, many other shapes in geometry and the flat option only wins by elimination when all those shapes have also been eliminated.

It is at this point that a skeptic can argue that one can never be sure that all the options have been considered, so one can never know that the right explanation has been found. After all, the skeptic can say, the right explanation might not even be in the competition. This fact is sometimes used by conspiracy theorists to cast doubts on an accepted explanation. This explanation might be the best among the known explanations but is not the true explanation. Unfortunately for the conspiracy theorist, this same doubt also applies to their conspiracy theory, so they need more than skepticism to support their own explanation.

While the skeptic might be right about the impossibility of certainty, it is still possible to hold the competition between the known explanations while keeping in mind that alternatives have been missed. But the mere fact that there could be missed alternatives does not itself show that a good explanation has not been found. To use an analogy, think of a career. While there might be a better match for a person out there, this does not entail that their current career is not a good one (or even the best). After all, the career can be assessed by various standards and against the known alternatives. The same holds for explanations. So, while the possibility of unknown explanations should be kept in mind, their mere possibility should not be taken as refuting an explanation.

 The second challenge is that of establishing the second premise—eliminating the competition.

To the degree that the elimination of the other explanations is in doubt, the truth of the second premise remains in doubt. This leads to the matter of how explanations compete, which is the subject of the next essay in this series.