Circular Argument

Circular arguments are often encountered in genealogy.

TheWikipedia describes it as "circular reasoning":

Circular reasoning is the basing of two conclusions each upon the other (or possibly with more intermediate steps). That is, if you follow a chain of arguments and conclusions (a proof or series of proofs), one of the conclusions is presumed by an earlier conclusion.

Circular arguments in genealogy can be quite simple, often taking the form

A is B

B is C

therefore C is A

In many cases, the use of such logic patterns is reasonable. For example

Example 1:

1) George Washington married a woman named Martha

2) Martha's father was John Dandridge

3) Therefore Martha's maiden name was Dandridge

As it happens, the above is entirely correct [See wikipedia:Martha Washington], though the argumenation is incomplete. If one wished, one could cite specific primary sources that demonstrate the truth of both points 1 and 2, as well as the correctness of point 3.

Consider the following variation

Example 2:

1) George Washington married Martha Custis

2) Her father's first name was John

3) Therefore Martha's father was "John Custis".

While point 1 of example 2 seems to contradict point three of the example 1, both points are true. This is because Martha was a widow when she married George Washington, and her full name could have been styles "Martha Dandridge Custis". Either "Martha Dandridge" or "Martha Custis" can be legitimately used to identify George Washington's wife. What's not correct is the conclusion in example 2 that Martha's father was "John Custis"; he was, in fact, "John Dandridge".

The reason the logic scheme in example 2 goes wrong is because there's an assumption being made that's not supported by fact---namely that because Martha surname at marriage was "Custis" her father's surname must have been "Custis". The missing element of logic is that "Custis" was Martha's married name.

Circular arguments such as this can be quite difficult to recognize, particularly in genealogy. This is in part because many genealogists routinely avoid giving detailed explanations for their conclusions, and "facts" are presented with little if any attempt at qualification or documentation. When facts are divorced from the underlying context and sources, a breeding ground for circular arguments arises.