Genealogical fallacies in logic

When I was in high school I took a course called “Theory of Knowledge.” I may have enjoyed this course more than any other course I had ever taken up to that point and since (right up until I took Course 4 at the Institute of Genealogy and Historical Research).

One of the course units dealt with classical logic, and logical fallacies. I recently found a handout on “Logical Fallacies” that I received in the course. Sadly I cannot produce a “full and accurate” citation to this handout, as I can’t remember details from nearly twenty years ago.

Much of scholarly genealogical research involves the use of logic–deductive and inductive reasoning. Many of the errors that occur in research similarly result in fallacies of logic. I would like to discuss the most common fallacies, as described on this twenty-year-old high school handout, here.

First the definition of a fallacy:

Fallacies are mistakes in reasoning.

A fallacy is an error in reasoning or in an argument. As such they are not rational in the true sense of the word. Most people who commit fallacies do so out of carelessness or haste. Many people who use fallacies are trying to side-step pure reasoning and manipulate others through psychological techniques. There are hundreds of different fallacies, but a few are listed below:

Not only does this definition address fallacies in a simplified way, it also demonstrates that many of the most common genealogical mistakes are directly caused by fallacies. The small selection of fallacies that I have extracted from the handout for this blog post below further demonstrate this connection between genealogical error and poor reasoning:

1. Hasty generalization – Drawing a conclusion (inference) on insufficient evidence.

2. Dicto simpliciter – Not taking genuine exceptions into account.

. . .

5. Circular reasoning – Going around in a circle – using the premise as the conclusion and vice versa – sometimes called “begging the question.”

6. False cause – supposing that two things that are connected by coincidence somehow cause each other.

. . .

8. Ad ignorantium – drawing a conclusion with no evidence one way or the other.

. . .

11. Appeal to authority – trying to get your position accepted because an authority says so when the authority is irrelevant to the issue.

12. Composition – Assuming what is true of the parts is true of the whole and vice – versa – what is true of the whole is true of the parts.

To demonstrate some of these fallacies, let us examine a few scenarios a genealogist might come across:

1. Hasty Generalization. Susan Smith, age 12 years, appears in the 1860 federal census in the household of Richard Smith, age 36 years. The fallacious conclusion would be that Susan Smith is the daughter of Richard Smith, with no further evidence to support it. The 1860 federal census does not provide family relationships, so any conclusion involving family relationships based on this evidence constitutes a fallacious argument.

2. Dicto simpliciter. Alexander Brown, an African American man, appears in the 1870 federal census in Mississippi. A genealogist falling prey to this fallacy would not even look for Alexander in the 1860 federal census, assuming that he was enslaved until the Civil War. The presence of free people of color in Mississippi (though relatively few) constitute “genuine exceptions.” The possibility that Alexander Brown was free in 1860–perhaps in another locality, migrating as a soldier during the War itself–exists.

8. Ad ignorantium. This fallacy is probably the most rampant in genealogy. Suppose family tradition says that your great-grandfather James Lee was related to Robert E. Lee. No connection is found. Or you great-great-grandmother Beatrice Jones was a “full-blooded American Indian.” Again, no evidence suggests this conclusion. Believing what you want to believe despite a lack of evidence is this fallacy in a nutshell.

11. Appeal to authority. A published family history says that William Mulliken came from  West Virginia. The fallacious conclusion would accept this statement as gospel, without further research. Just because it’s in print–even if the author is a well-respected authority–doesn’t mean its true.

We are all guilty of nearly all of these fallacies at one point or another in our career.

Do you have any other examples that immediately come to mind?

If you would like to cite this post:

Michael Hait, CG, “Genealogical fallacies in logic,”Planting the Seeds: Genealogy as a Profession blog, posted 19 December 2012 (https://michaelhait.wordpress.com : accessed [access date]). [Please also feel free to include a hyperlink to the specific article if you are citing this post in an online forum.]