Grice's Conversational Maxims

Quality

Be Truthful

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

Quantity

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.

Relation

Relevance

• Be relevant.

Manner

Be Clear

• Avoid obscurity of expression.
• Avoid ambiguity.
• Be brief (avoid verbosity).
• Be orderly.

This list is based on http://en.wikipedia.org/wiki/Gricean_maxims