Griceian Desirability

From an Oxford U. P. site:

"Grice continues his project of proving the univocality of common modals (the ‘Equivocality Thesis’) by showing how a univocal structural representation can be applied to a certain (non-moral) class of alethic and practical acceptability statements that are at least sometimes (informally) valid, subject to license of the involved transitional inferences from a ‘Principle of Total Evidence’."

"Grice also shows that these acceptability statements can be modified to account for defeasible (ceteris paribus, degrees of probability/desirability) and non-defeasible (‘unqualified’) generalizations, which in turn can be utilized to account for a univocal set of modals such as ‘ought’ and ‘must’."

"The chapter closes with a discussion of the ‘Principle of Total Evidence’."