 Most authors who write about the norm of assertion appeal to their own intuitions. However, this is an area where experimental data is highly relevant. If the aim is to describe a real-word communicative act, rather than a purely idealized philosopher’s construct, it follows a good theory of assertion should make predictions that are consistent with our actual practice: it should deem appropriate the assertions that ordinary speakers deem appropriate, and inappropriate the ones that they criticize as inappropriate. If this is right, competing accounts can be tested empirically against the intuitions of competent speakers of the language.