Orthodoxy in the contemporary debate on knowledge ascriptions holds that the truth‐value of knowledge ascriptions is purely a matter of truth‐relevant factors. One familiar challenge to orthodoxy comes from intuitive practical factor effects . But practical factor effects turn out to be hard to confirm in experimental studies, and where they have been confirmed, they may seem easy to explain away. We suggest a novel experimental paradigm to show that practical factor effects exist. It trades on the idea that people retract knowledge attributions when practical factors shift. We also explain why the resulting data raise a serious challenge to orthodoxy.