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Conspiracy theories on the basis of the evidence


Conspiracy theories are often portrayed as unwarranted beliefs, typically supported by suspicious kinds of evidence. Yet contemporary work in Philosophy argues provisional belief in conspiracy theories is—at the very—least understandable (because conspiracies occur) and if we take an evidential approach—judging individual conspiracy theories on their particular merits—belief in such theories turns out to be warranted in a range of cases. Drawing on this work, I examine the kinds of evidence typically associated with conspiracy theories, showing that the evidential problems typically associated with conspiracy theories are not unique to such theories. As such, if there is a problem with the conspiracy theorist’s use of evidence, it is one of principle: is the principle which guides their use of evidence somehow in error? I argue that whatever we might think about conspiracy theories generally, there is no prima facie case for a scepticism of conspiracy theories based purely on their use of evidence.

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  1. 1.

    Whilst Cassam seems willing to admit that conspiracies occur (see Warburton and Cassam 2015), he uses the terms ‘conspiracy theory’ and ‘conspiracy theory’ in the pejorative sense in the works discussed here.

  2. 2.

    For another analysis of Cassam’s work, see Pigden (2016).

  3. 3.

    For further criticism of Cassam’s argument see Dentith (in press).

  4. 4.

    This issue will be addressed in more depth come Sect. 8.

  5. 5.

    There is a common species of selective evidence in detective fiction: evidence so easily obtained it becomes obvious something has been removed/deleted/redacted in order to avoid awkward questions. Arguably this kind of evidence manipulation was central to the rationale as to the necessity of the invasion of Iraq in 2003; evidence of those pesky weapons of mass destruction was so easily found, yet when investigated the evidence had the hallmarks of having been curated/manipulated.

  6. 6.

    The obvious retort here would be to find examples of unprincipled citation of evidence by conspiracy theorists. However, we will find similar examples in the seemingly non-conspiratorial works of historians, scientists and politicians. Indeed, the existence of these examples are often fodder for the conspiracy theorist and her theory.

  7. 7.

    For an analysis of the arguments as to whether conspiracy theories are in some sense unofficial, and thus rival to official theories, see Dentith (2014, ch. 7) and Dentith (2016).

  8. 8.

    The corollary of this is that explanations in these domains which are not fuzzy—and thus take into account all the evidence—are likely post facto in nature.

  9. 9.

    A point pressed by Coady (2006).

  10. 10.

    As Sissela Bok defines it: ‘[A] neologism that stands for the spreading of false information to hurt adversaries’ (Bok 1982, p. 187).

  11. 11.

    This point has also been discussed by both Steve Clarke (2002), and Basham (2011).

  12. 12.

    For further discussion of this, see Basham (2011) and Dentith (2016).

  13. 13.

    Such judgments will differ from country to country, or culture to culture. We might, for example, suspect Aotearoa (New Zealand) to be a relatively benign polity compared to Romania. As such, New Zealanders might think of their country as unconspired because whilst conspiracies do occur, they occur infrequently compared to other nation states.

  14. 14.

    For further discussion on prior probabilities and allegations of conspiracy now see Basham (2011) and Dentith (2016).

  15. 15.

    The most remarked upon (and only alleged) false flag operation was the Reichstag Fire of 1933, which was used by the Chancellor of Germany, Adolf Hitler, to enable emergency legislation which suspended civil liberties and allow him to round up the suspected arsonists, the Communists. This curious and convenient fact has led some to argue that the fire was a false flag event, designed to bolster the power of the Nazis in the German parliament.

  16. 16.

    It is possible in such a situation that weak evidence is treated as being strong due to effects like confirmation bias and the like; we do not have to necessarily assume a conspiracy in such cases.

  17. 17.

    Barkun is no sceptic of conspiracies, and he accepts that some conspiracy theories have turned out to be warranted; here we are simply speaking about one aspect of his work.

  18. 18.

    This kind of size criterion can also be found in the work of Juha Rikk, who distinguishes between local, global and total conspiracy theories (Räikkä 2009); Martha Lee, who also talks about superconspiracies (Lee 2011); and Volker Heins, who also makes a similar distinction between types of conspiracies (Heins 2007).

  19. 19.

    This view on the rationality of what Barkun calls ‘event conspiracies’ can be found in earlier works by Pigden (1995), Keeley (1999), Knight (2000), and Basham (2001).

  20. 20.

    Such as taking control of a nation state or subverting existing institutions.

  21. 21.

    Superconspiracies, citing ever larger conspiracies, cast into doubt any evidence for the conspiracy, since the conspirators are considered to be in the position to control and subvert the evidential record.

  22. 22.

    Barkun’s stipulation about the irrationality of belief in systemic and superconspiracies is close in kind to Popper’s stipulation about the irrationality of belief in what he calls the ‘conspiracy theory of society,’ (Popper 1969); both Barkun and Popper ascribe to the kind of people who believe in all-embracing conspiracy theories a kind of mental pathology.

  23. 23.

    ‘Quickly’ here is measured in five year chunks.

  24. 24.

    Grimes does suggest that as time passes, conspirators are likely to start panicking about potential exposure, and thus leak regardless.

  25. 25.

    It is useful to note that Grimes labels Moon landing hoax theories as ‘fringe,’ climate change conspiracy theories as ‘utterly negated by the sheer wealth of evidence against such a proposition’ (Grimes 2016, p. 3), and anti-vaccination beliefs as ‘scare-mongering (Grimes 2016, p. 3).’ As such, Grimes starts out by assuming that which he wants to prove; these putative conspiracies are unviable.

  26. 26.

    For further discussion on this topic, see Dentith and Orr (2017).

  27. 27.

    For example, institutionalised racism and sexism, historically, has been brought to the public’s attention but not acted upon/been politely ignored. For the victims of such discrimination, at least, this can look very much like a society trying to cover things up and act as if everything is normal.

  28. 28.

    This, at least, was the rationale behind the cover-up of the ‘Unfortunate Experiment’ in Aotearoa (New Zealand), where women who had been diagnosed with cervical cancer were not informed that they were taking part in a clinical trial and being deliberately under-treated. The whistleblowers were ignored by the authorities because to act upon that information would have lead to a loss of trust by the public in the medical profession.

  29. 29.

    As previously mentioned, see Dentith (2016).

  30. 30.

    Indeed, many of the activities we suspect ground our belief in the existence of conspiracies are open secrets, some of which we just politely ignore, or downplay (see Dentith and Orr 2017).


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Thanks to Daniel Wilson, Lee Basham, Martin Orr, Richard Viskovic, and Tiddy Smith for feedback on an early draft of this paper, as well as the participants and audience at the SCIENCONS conference and workshop (November 2016) at the University of Padova for feedback on elements which made it into this paper.

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Correspondence to M R. X. Dentith.

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M R. X. Dentith was supported by a fellowship at the Research Institute of the University of Bucharest (ICUB).

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Dentith, M.R.X. Conspiracy theories on the basis of the evidence. Synthese 196, 2243–2261 (2019).

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  • Conspiracy
  • Conspiracy theory
  • Evidence
  • Disinformation
  • Errant data
  • Prior probabilities