Effective communication requires being truthful, informative, relevant, and clear.
Grice's 1975 maxims of quantity, quality, relation and manner. Their real interest is in violation: deliberately flouting one is how implication and irony work.
In practice
- A status update that is technically true, relevant and clear, and omits the thing the listener needed, has violated quantity while satisfying the rest.
- A witness who answers exactly what was asked and nothing more is obeying quantity and using it as a weapon.