H. P. Grice's Desideratum of Conversational Clarity

H. P. Grice's  desideratum of conversational clarity concerns the manner of expression.
 
[His later reference to Modus as used by Kant as one of the four  categories]
 
for any conversational contribution.
 
It includes the
 
              IMPORTANT
 
expectations of relevance to understanding and also insists
that the main import of an utterance be clear and explicit.