Knowing from Words

No one disputes that much, probably the greater part, of our knowledge is derived from hearing what others say or reading what others have written. It is also indisputable that much, though not all, of what we thus hear or read we accept without question as true. In brief, a great part of our systems of belief rests upon testimony. The question is whether we are to regard testimony, so understood, as a direct and immediate source of belief based upon it or whether we are to regard belief so based as being, in the last resort, essentially the product of other, more fundamental sources of knowledge, or, in brief again, is testimony, as a source of knowledge (or belief), reducible to these other sources?