Why are contemporaneity and feasible meeting distinguished?

Muʿanʿan Transmission: Possible Meeting, Evidence of Hearing, and Continuity

• Living in the same era itself proves direct hearing in every claimed link
• Contemporaneity may be established while other historical facts rule out a feasible encounter
• Feasible contact eliminates every possible hidden defect in a report
• Possible contact depends only on reliability, never on historical circumstances