Paul Grice's "conversational cooperation" maxims;
2. Take care not to say false things.
3. Be relevant (stick to the topic, etc.)
4. Be perspicuous (clear, orderly, brief, and so on)
Paul Grice (1913-1988), a British philosopher, was best known for his original work in philosophy of language. Grice wrote on several philosophical subjects, including metaphysics and ethics.