Our early clinical studies applying the two-factor approach to delusions had focussed primarily on single cases of monothematic delusions with seemingly fantastic belief content (e.g., Capgras delusion; the delusional belief that a loved one has been replaced by a visually similar impostor). We aimed to show that people who profess such beliefs are not so different from the rest of us by discovering the first-factor disruptions to basic cognitive processes (e.g., for identifying familiar faces) that distort these individuals’ experiences and explain the generation of their delusions. Later, we began to study shared delusions, or cases of ‘folie à deux’ (Langdon, 2013). The so-called ‘secondary’ (person) in these cases experiences no disruptions to basic cognitive processes that would explain the generation of the shared delusion; instead, they simply come to accept what the ‘primary’ (usually a person of influence) tells them. Since this is precisely how we acquire most of our beliefs about the world, we began to examine other socially transmitted non-clinical, yet sometimes ‘troublesome’, beliefs (e.g., conspiracy theories). Professor Ryan McKay and colleagues continue to study other prominent beliefs seen in society today: Does God exist? Are genetically modified foods safe? Did Trump collude with the Russians? (e.g., Tappin, van der Leer & McKay, 2017). Different biases shape the beliefs we entertain about these questions and how we gather and evaluate evidence. Future work will continue to uncover the psychological, social and evolutionary causes of these biases and examine their consequences.