From Ibn Khaldun: The Muqaddimah~
Many competent persons and expert historians have erred in regard to such stories and opinions, and have acceptd them without critical examination, and therefore history has been confused.

He who practises this science needs to know the rules of Statecraft, the Nature of Existing Things, and the Difference between: Nations, Regions and Tribes In Regard To Way Of Life. Qualities of Character, Customs, Sects, Schools of Thought, and so on.

He must distinguish the similarities and differences between the Present and Past, and know the various origins of Dynasties and Communities; the reasons for their coming into existence, the circumstances of the Persons involved in them, and their History!

He must go on until he has complete knowledge of the Causes of EVERY event, and then he will examine the information which has been handed down in the light of his principles of explanation. If they are in Harmony, this Information is Sound.