Abstract

Psychological states and illnesses share an important epistemic feature with conspiracy theories: Both do not exist in rem. They are multiform and fuzzy phenomena, not completely understood, and all diagnoses are ascriptions. What is depression? What is intelligence? And, likewise: What is a conspiracy theory, how do we spot it, and how are we able to measure the belief in it? The problem of measuring vague and not directly observable concepts was and is one of the major challenges in academic psychology. This chapter outlines benefits and downsides of the psychometric approach. It is argued that current approaches for diagnosing belief in conspiracy theories are insufficient. They suggest an accuracy in measurement that is impossible given the fuzziness of the construct that is to be measured. They also neglect the cognitive and emotional dynamics behind acquisition and propagation of conspiracy theories. However—these drawbacks in mind—we should not refrain from devising and improving tools and methods that are able to quantify aspects of the belief in conspiracy theories. Used reasonably, they open up the possibility to enrich epistemic discussions with empirical findings.