History questions?

[Red Harvest]

I have a question that has been nagging me, when does a source becomes credible and when does it not?

What makes it credible for instance? and how does it become credible?

I think this is history related, if not please move.

I don't know what the technical definitions are, so this is my layman's interpretation, but some criteria that seem to be typically used to weigh a source:
1. Is the information first hand?
2. Is it 2nd hand, but a close associate/confidant etc.?
3. Is it at least contemporary?
4. Is there anything corroborating the source's info? (Physical/geological evidence, written evidence from a different perspective, letters, etc.)
5. Has the source been shown to have bias in one way or another (where it is relevant to the topic?)
6. Has the source been found credible in most/all other instances where verification was possible? That is probably the biggest factor.
7. Does the source have a stake in the matter that might encourage them to skew the truth? (They might be 100% reliable on topic A, and not so much on topic B.)
8. Did contemporaries consider the source credible?

One of the best proofs of credibility in my mind is when a source says something that is counter to the prevailing wisdom, yet their "improbable" story is later proven true through some shrewd detective work.

We have to remember, three people can see the same event, yet come up with three completely different conclusions; and yet what the three describe might be accurate from the perspective each was viewing. (It is similar to officiating, each person will be in a different position to make a call--they have to call it as they see it, doesn't mean they are lying or biased if the call goes against them when reviewed on tape, often they are not in position, or not watching the correct point to make the call.)

[Leet Eriksson]

Much thanks my friend.

[Pericles]

In addition to the excellent info by Red Harvest, one should often read several books and see several documentaries on the period in question.

Especially, take careful note of the author's credentials. Someone who is a professor of history at Oxford and is well known for writing history books will often be more knowledgeable and credible on a subject, than someone else who might be writing on the same subject but who has far less education and who may have a stake in the argument and is slanting the history to conform to his viewpoint.