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Proof-Evidence Classroom

Proof - What is it?

A common misconception among genealogists is that "proof" is some kind of an absolute - that its use establishes a certainty which can never be refuted. A statement often made goes like this: "John Jones is the father of Tom Jones, and I have the proof." That is a questionable use of the word proof, considered by some to be incorrect. The statement uses "proof" as if it were synonymous with "evidence", when in fact proof is the use of evidence. In his book, The Nature of Proof, Erwin P. Bettinghaus defines proof as, "the process of using evidence to secure belief in an idea or statement."(1) Thus we see that proof is only as good as the evidence used. To say that you have "proved" your lineage to a Revolutionary ancestor merely means that you have used evidence to establish your belief that the lineage is correct.

Besides evidence, the other key word in the definition of proof is "belief". Bettinghaus defines belief as, "any simple proposition that an individual can attest to."(2) Perhaps clearer is the following: Belief is an idea that someone holds to be true or factual. The important point is that a belief is a very subjective thing, a type of individual judgment. Therefore, the strength of a proof might well depend upon who you are able or might be able to convince with your evidence. If the leading genealogist in the country accepts a lineage, the proof of the lineage is apt to be sound. Because he is an authority on such matters, his beliefs will carry much weight. Nevertheless, it must be remembered that even the belief of an accepted authority does not establish certainty. The only thing that is certain is that the lineage is either correct or it isn't.

How, then, are we to know who our parents are? Perhaps the word "to know" is a little stronger than "to believe". The dictionary only leads us in circles. To know is to be sure; to be sure is to be confident; to be confident is to be certain or sure. Can you prove who your parents are? That is, can you use evidence to secure belief that John and Mary are your parents? Certainly, you say, and you proceed to list the following:

Such statements are a list of evidence and nothing more. And they should lead to the belief (by anyone who "believes" you are truthful) that John and Mary are indeed your parents.

As insecure as it may make us feel, we must learn to live with uncertainty in our genealogical work. The validity of any pedigree connection between generations is merely a probability. It is a probability because we are not dealing with iron clad logic, but with subjective judgments. The implications are a little startling. For example, the probability that a given individual is indeed your ancestor decreases with each succeeding generation back in time. To see why this is so requires a little probability theory from the field of mathematics. Let us assume that the probability that each link in a pedigree is correct is .90 (1.00 is certainty) or 90%. A 90% probability accumulated over ten generations would lower the probability that all connections are correct to only 35%. Another way of saying the same thing is that there is a 65% likelihood that the man who you believe to be your 8th great grandfather really isn't! (That is, given the assumptions above.)

The actual probabilities are, of course, not known to the present writer and would be complex to determine. They might be above .90 in some instances. With scanty evidence the probability would be lowered to far below .90. There is one consolation, however. The probability that any random individual is your ancestor increases with time. It is almost a certainty that William the Conqueror is your ancestor if you have much English blood. Genealogy becomes the history of a race after a few centuries.

There are many hidden assumptions in genealogical work. These assumptions account for much of the uncertainty which arises. One such is the question of legitimacy, a point well made by the late Donald Lines Jacobus in an article entitled, "Certainty in Genealogy", which he published some years ago. If any form of inference, such as a logical deduction, is used as proof, the validity of the assumptions as well as the validity of each step in the deduction must be considered. The following example is given so that the reader can look for the hidden assumptions and can better understand the nature of proof in genealogy.

STATEMENT: John Williams was the father of Elizabeth Williams.



Much of the evidence given in #1 - #6 is circumstantial, which, however, is convincing in support of the original belief.


THE BELIEF WHICH RESULTS: John Williams was the father of Elizabeth Williams.

The foregoing is nothing less than a formal proof that Elizabeth Williams was the daughter of John Williams. The reader might ask, why was it necessary to establish the identity of Elizabeth and John? Identification is the use of facts to establish with high probability the identity or uniqueness of a specific person. Vital statistics (birth, death, marriage) are frequently used because they are commonly available. These facts label a person as unique. Banks ask for name, birthdate and birth place, and mother's maiden name because it is almost impossible for two people to have these same statistics attached to them.

Identity of an individual is one of the hidden assumptions which were formerly discussed, and one which commonly causes grave errors to occur in genealogical work. The fewer facts known about an individual, the greater the likelihood that he is not unique, and that he can be confused with someone else. Thus we see the importance of learning everything possible about our ancestors - especially in the absence of vital statistics. Facts should be gleaned from every possible source. Such a procedure increases in importance as the frequency of occurrence of the name increases. In the Southern states such meticulous research often is necessary due to the lack of public vital statistics.

In the proof given above it was assumed that the dates and places listed for identification were indeed correct. Without realizing it we go through a process of proof anytime we attach a date to someone's name. Of course, the dates in and of themselves have no significance. They are important because they often help with identity and therefore help to prove pedigree connections. There are assumptions relative to the evidence proving Elizabeth to be a daughter of John Williams, first that all the evidence is accurate, and second that is relevant. Nevertheless, the proof does exist, and does indeed establish a belief in the mind of the present writer, at least, that the claimed relationship is a true one. Belief in this case leads to action - the writer will continue in his search for the wife and ancestry of John Williams, believing as he does that John is his 3rd great grandfather.


Copyright © 1976-2006 by William A. Yates. All rights reserved.

Copied and published with the permission of:
Bill Yates
Yates Publishing
P.O. Box 67
Stevensville, MT 59870
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Updated: December 11, 2008.