Paul Grice, the philosopher, proposed four conversational maxims that arise from the pragmatics of natural language. These maxims are:

Maxim of Quality:

 - TRUTH
 - Do not say what you believe to be false.
 - Do not say that for which you lack adequate evidence.

Maxim of Quantity:

 - INFORMATION
 - Make your contribution as informative as is required for the current purposes of the exchange.
 - Do not make your contribution more informative than is required. 

Maxim of Relation:

 - RELEVANCE
 - Be relevant. 

Maxim of Manner:

 - CLARITY
 - Avoid obscurity of expression.
 - Avoid ambiguity.
 - Be brief (avoid unnecessary prolixity).
 - Be orderly.