A note raises an objection: reports are fallible, so how can transmitted knowledge supply demonstrative premises? It responds by considering the rational grounds and corroborative conditions that can make particular reports convincing.
The point is not that every transmitted assertion is certain. Rather, the traditional theory holds that reports meeting sufficiently stringent conditions can function as sources of certainty.
When assessing an actual report, separate the original event, the number of apparent reports, and the real independence of their sources.