Grice's Maxims 

The Maxim of quality - where one tries to be as informative as one possibly can, and gives as much information as is needed, and no more. 

The Maxim of quality - where one tries to be truthful, and does not give information that is false or that is not supported by evidence. 

The Maxim of relation -  where one tries to be relevant, and says things that are pertinent to the discussion.

  The maxim of manner -   when one tries to be as clear, as brief, and as orderly as one can in what one says, and where one avoids obscurity and ambiguity