Is There Anyone else out There? A Measure of Psychological Solipsism

For centuries philosophers have debated solipsism, the idea that people cannot prove that anything exists outside of their own minds. However, there have been few investigations of psychological solipsism, which is doubt, experienced by people in their everyday lives, that others exist outside of their own minds. We suggest that psychological solipsism is a problem experienced by a nontrivial number of people with negative personal and interpersonal consequences. To test this hypothesis, we developed a new self-report measure of psychological solipsism (MSol). In seven studies (five pre-registered, N = 2633) we found that the MSol had acceptable internal consistency, test-retest reliability, discriminant validity, and predictive validity. Psychological solipsism was associated with loneliness and a lack of social connection, as well as problematic video game playing. The results were also consistent with the hypothesis that psychological solipsism predicts aggressive tendencies. We point to several avenues of further research, such as pursuing the relationships between psychological solipsism, problematic video game playing, and aggression.