I did not just show that you can’t prove a negative.

I did not just show that you can’t prove a negative.

A Peculiar and Perpetual Tendency: An Asymmetry in Knowledge Attributions for Affirmations and Negations

Turri, J. (in press). A peculiar and perpetual tendency: an asymmetry in knowledge attributions for affirmations and negations. Erkenntnis.



From antiquity through the twentieth century, philosophers have hypothesized that, intuitively, it is harder to know negations (i.e. claims about what is not) than to know affirmations (i.e. claims about what is). This paper provides direct evidence for that hypothesis. In a series of studies (N = 1132), I found that people naturally view negations as harder to know than affirmations. Participants read simple scenarios and made judgments about truth, probability, belief, and knowledge. Participants were more likely to attribute knowledge of an outcome when framed affirmatively than when framed negatively. Participants did this even though the affirmative and negative framings were logically equivalent. The asymmetry was unique to knowledge attributions: it did not occur when participants rated truth, probability, or belief. These findings show new consequences of negation on people’s judgments and reasoning and can inform philosophical theorizing about the ordinary concept of knowledge.


John Turri