I've taken some heat from partisans on both sides of the Book of Mormon debate for not accepting various proposed parallels to the Book of Mormon. For example, I don't believe that the Book of Mormon plagiarized from Ethan Smith, Solomon Spalding, Mercy Otis Warren, or Shakespeare. On the other hand, I also don't believe that the Book of Mormon is directly connected to Orphism, Asherah-worship, or ancient Hebrew literary forms. My skepticism has earned me the ire of some who believe the parallels between the Book of Mormon and these other works/authors/traditions make direct dependence undeniable.
But my caution about drawing hard conclusions from such parallels comes from hard experience and careful study. It actually might be rather shocking to the non-historian to realize just how often parallels occur by accident or independent invention rather than direct borrowing. Historians must be extremely careful about assessing the meaning of parallels. (See Ben McGuire's article here for a good discussion of the issue.)
So how do we evaluate the significance of parallels? Here are some questions I usually ask myself:
1) Can we establish a direct link between the two texts?
In linking 19th century texts to the Book of Mormon, this means we have to evaluate the plausibility and the probability that the author of the Book of Mormon had read the 19th-century text. If there is no direct evidence of a connection, then the value of the parallel is significantly diminished.
In studying ancient parallels, this means that we have to judge how probable or plausible it is that the Mulekites came to have the word sheum 2000 years after the word went out of usage in the Middle East. It means we have to judge how probable or plausible it is that medieval Christian and Muslim legends about Abraham came to record accurate details of his life. If we cannot establish a chain of evidence across the millennia, then the significance of such parallels is significantly diminished.
2) Can we establish the direction of dependence?
This is a problem, for example, in Lucy Smith's reminiscence of Joseph Smith, Sr.'s tree of life dream. Which was dependent on the other? The Book of Mormon on the dream or the telling of the dream on the Book of Mormon? Or does the dependence perhaps go both ways? Sometimes the direction of dependence simply cannot be determined with any probability.
3) Is it possible that instead of direct dependence, there is mutual dependence on a third source?
I have found that in many instances where there is a purported parallel between JS's scriptures and ancient apocrypha or midrashim, the parallel is more likely due to the two texts' mutual dependence on the Bible. Similarly, the purported similarities between the Book of Mormon and View of the Hebrews or the Spalding Manuscript may be due to their mutual dependence on contemporary speculations that circulated through the oral culture of New York.
4) Is it possible that the dependence of one text on the other is mediated through a third source?
Although similarities can be found between the writings of Joseph Smith and theological or historical works of his day, we also have to remember that his culture was largely oral culture. He probably got most of his theology from sources like sermons or his Methodist class meetings. Similarly, parallels to the ancient mysteries may have been mediated through Masonry, the occult, or the Bible.
5) What is the "strength" of the parallel?
I have found that accidental parallels are far more common than one might think, and parallels often appear deceptively "strong" when in fact they are quite weak.
When we can use quantitative or experimental methods to determine the likelihood of parallels emerging by accident, we should. A while back some friends and I created a quantitative methodology for judging the significance of Hebrew names in the Book of Mormon. That method has not yet been applied. Similarly, I believe that one could judge the likelihood of the Anthon characters accidentally paralleling Demotic or Meroitic if one were to ask people with no knowledge of Egyptian to write out a series of made-up Egyptian characters and then see if parallels can be found. The Edwards and Edwards study of chiasmus went a long way toward convincing me of the intentionality of Book of Mormon chiasmus, though the methodology of that study was not airtight. There are quite a few cases where experimental and quantitative rigor could help bring a measure of objectivity to the discussion.
Unfortunately, in many cases a quantitative approach is simply not possible or practical. In these cases experience is the best guide. The historian who has chased down hundreds of false parallels will hopefully eventually develop an eye for the significant ones. Questions I ask myself are, "could these authors have come to the same conclusions or motifs independently?" "Is there evidence of independent development or invention of these ideas?" Independent invention is surprisingly common throughout history. Certain ideas are simply practical, reasonable, or archetypally appealing, and so humans arrive at them independently for similar reasons. It is also worthwhile to ask how many points of similarity there are, how close and complex are the parallels, and what are the major points of difference. We should not make too much of differences, of course. They rarely disprove dependence, since borrowers have their own agendas and thus can hardly be expected to robotically reproduce all of their source's ideas without modification. But they can raise doubts about it. And if borrowing is occurring, they can be very revealing as to the borrowing author's mind and motivation. In particular, he may be subverting or modifying his source material in very deliberate ways.
