Final answer:
Geoffrey Ashe suggests that King Arthur's conquests lack historical documentation due to a bias against oral tradition, leading to an overreliance on written records which are scarce for that period.
Step-by-step explanation:
Geoffrey Ashe, in the “Conversation with Geoffrey Ashe,” mainly identifies the lack of historical documentation for King Arthur's conquests as a result of an over-reliance on written material and a bias against knowledge presented via oral tradition. This implies that while the historical events of King Arthur's era may have been well known and documented through oral histories, these narratives were not given the same credibility as written records. As a consequence, the stories and achievements of King Arthur that were passed down through generations by word of mouth were not formally recorded in texts that have survived to the present day, leading to a scarcity of historical documentation.