When is an interpretation definitive, is Ijtihad permissible in it, and when is its meaning impossible?

Interpretation relies on definitive texts such as the Qur’an and authentic Sunnah. It is impossible for the inferred meaning to contradict what is stated in the Qur’an or Sunnah, because Allah is the most truthful of speakers, and His words do not contradict each other. Contradiction in the Qur’an is when two verses oppose each other in such a way that one prevents the meaning of the other. This does not occur between two verses whose meanings are informative, because it would necessitate falsehood, which is impossible concerning Allah.