H. P. Grice's Principle of Conversational Fortitude

FORTITUDO – Grice’s strength -- A FORTIORI: a fortiori: L. for a stronger reason, even more so or with more certainty, an argument that if everything that possesses A will possess B, then if a given thing possesses A to a greater degree, it has a stronger reason (a fortiori) to possess B. For example, if all old men who are healthy can run, then a fortiori a young man who has greater health than old men can run. “All the so-called relational (or a fortiori) syllogisms depend on the transitivity of the relations.” Cohen and Nagel, An Introduction to Logic and Scientific Method.