score:4
IMO there is no number that can be specified as sufficient. Everything depends on the nature of the evidence and the sources presented:
In one case, we may have only one eyewitness account from a historical actor or witness, or one archeological artifact that is accepted as valid, and that may be enough to stand as historical proof.
In another case, we may have little or nothing in the way of good primary sources, and must accumulate many pieces of evidence, sometimes circumstantial, sometimes from sources of somewhat questionable reliability, until we build a case based on preponderance of evidence, as Samuel Russell has quite aptly explained.
Borrowing from other disciplines, we find three different thresholds of acceptable proof:
History most of the time is not nearly as clear cut as Science or Criminal Law. (The fact that this question has been asked is probably sufficient proof of that...) It is most akin to Civil Law in the threshold of proof required, since oftentimes no more is possible, particularly when dealing with events of the distant past. And so when dealing with History, any, (or certainly all) of the above will suffice, depending on the available sources and the manner in which they are presented.
Needless to say, the inviolability of any historical proof will depend on the strength of the evidence: The further we deviate from scientific proof and move towards preponderance of evidence, the weaker the "proof" may be.
Upvote:9
The answer lies in history being a discursive and inductive practice where our evidentiary materials are untrustworthy. A preponderance of the evidence, correctly interpreted, with a correct interpretation of what constitutes relevant evidence is required. This is obviously debatable. My invaluable peasant letters are your irrelevant ephemera.
Proofs can't be offered inductively; only unrefuted conjectures.