Two Important Properties for Inference

• Soundness: If KB |- Q then KB |= Q
  That is, if Q is derived from a set of sentences KB using a given set of rules of inference, then Q is entailed by KB. Hence, inference produces only real entailments, or any sentence that follows deductively from the premises is valid.

• Completeness: If KB |= Q then KB |- Q
  That is, if Q is entailed by a set of sentences KB, then Q can be derived from KB using the rules of inference. Hence, inference produces all entailments, or all valid sentences can be proved from the premises.