Table of Contents
History of Philosophizing about Conspiracy Theories
Problems of Definition
Types of Conspiracy Theories
Criteria for Believing in a Conspiracy Theory
Criteria concerning Scientific Methodology
Internal Faults
Progress: Is the Conspiracy Theory Part of a Progressive Research Program?
Inference to the Best Explanation: Evidence, Prior, Relative and Posterior Probability
Errant Data
Criteria Concerning Motives
Cui Bono: Who Benefits from the Conspiracy?
Individual Trust
Institutional Trust
Other Realist Criteria
Fundamental Attribution Error
Ontology: Existence Claims the Conspiracy Theory Makes
Übermensch: Does the Conspiracy Theory Ascribe Superhuman Qualities to Conspirators?
Scale: The Size and Duration of the Conspiracy
Non-Realist Criteria
Instrumentalism: Conspiracy Theories as “as if” Theories
Pragmatism
Social and Political Effects of Conspiracy Theories
What to Do about Conspiracy Theories?
Related Disciplines
References and Further Reading
1. History of Philosophizing about Conspiracy Theories
Philosophical thinking about conspiracies can be traced back at least as far as Niccolo Machiavelli. Machiavelli discussed conspiracies in his most well-known work, The Prince (for example in chapter 19), but more extensively in his Discourses on the First Ten Books of Titus Livius, where he devotes the whole sixth chapter of the third book to a discussion of conspiracies. Machiavelli’s aim in his discussion of conspiracies is to help the ruler guard against conspiracies directed against him. At the same time, he warns subjects not to engage in conspiracies, partly because he believes these rarely achieve what they desire.

Where Machiavelli discussed conspiracies as a political reality, Karl Raimund Popper is the philosopher who put conspiracy theories on the philosophical agenda. The philosophical discussion of conspiracy theories begins with Popper’s dismissal of what he calls “the conspiracy theory of society” (Popper, 1966 and 1972). Popper sees the conspiracy theory of society as a mistaken approach to the explanation of social phenomena: It attempts to explain a social phenomenon by discovering people who have planned and conspired to bring the phenomenon about. While Popper thinks that conspiracies do occur, he thinks that few conspiracies are ultimately successful, since few things turn out exactly as intended. It is precisely the unforeseen consequences of intentional human action that social science should explain, according to Popper.
Popper’s comments on the conspiracy theory of society comprised only a few pages, and they did not trigger critical discussion until many years later. It was only in 1995 that Charles Pigden critically examined Popper’s views (Pigden, 1995). Besides Pigden’s critique of Popper, it was Brian Keeley (1999) and his attempt at defining what he called “unwarranted conspiracy theories” that started the philosophical literature on conspiracy theories. The question raised by Keeley’s paper is essentially the demarcation problem for conspiracy theories: Just as Popper’s demarcation problem was to separate science from pseudoscience, within the realm of conspiracy theories, the problem Keeley raised was to separate warranted from unwarranted conspiracy theories. However, Keeley concluded that the problem is a difficult one, admitting that the five criteria he proposed were not adequate for specifying when we are (un)warranted to believe in a conspiracy theory. This article returns to this problem in section 4.

After Popper’s work in the late 1960s and early 1970s, and Pigden’s and Keeley’s in the 1990s, philosophical work on conspiracy theories took off in the first decade of the 21st century. Particularly important in this development is the collection of essays by Coady (2006a), which made visible that there is a philosophical debate about conspiracy theories to a wider audience, as well as within philosophy. Since this collection of essays, philosophical thinking has been continuously evolving, as evidenced by special issues of Episteme (volume 4, issue 2, 2007), Critical Review (volume 28, issue 1, 2016), and Argumenta (volume 3, no.2, 2018).

Looking at the history of philosophizing about conspiracy theories, a useful distinction that has been applied to philosophers writing about conspiracy theories is the distinction between generalists and particularists (Buenting and Taylor, 2010). Following in the footsteps of Popper, generalists believe that conspiracy theories in general have an epistemic problem. For them, there is something about a theory being a conspiracy theory that should lower its credibility. It is this kind of generalism which underlies the popular dismissal, “It’s just a conspiracy theory.” Particularists like Pigden, on the other hand, argue that there is nothing problematic about conspiracy theories per se, but that each conspiracy theory needs to be evaluated on its own (de)merits.