If your theory explains the evidence does that mean it is probably correct? If “everything fits”, is your theory therefore surely right?
There’s a problem with that way of thinking and it is taken head-on by Paul Newall in a chapter titled “Logical Fallacies of Historians” in Tucker and Kane’s A Companion to the Philosophy of History and Historiography.
Affirming the consequent is a formal fallacy occurring when one or more potential premises are omitted from an argument. For example, “if my rain dance worked then it should be raining; it is raining; therefore, my rain dance worked.” Here other possible causes of the rainfall are left out and the argument fails. Affirming the consequent has the general form:
P1: If A then B;
C: Therefore, A.
Some of you may know of a 1970 “classic” by David Hackett Fischer, Historians’ Fallacies: Toward a Logic of Historical Thought. Newall acknowledges the strength of Fischer’s work but in a single chapter is addressing what he sees as the most common and unfortunately enduring fallacies among historians.
So how can one guard against being overcome by this fallacy? Newall continues:
However, we can add missing premises to show the error:
P1a: If C then B;
P1b: If D then B;
. . . and so on. For an argument of this form to not be fallacious, we would need an additional premise stating that A is the only possible cause of B. (Note that affirming the antecedent (or modus ponens) is not fallacious; that is, arguing “if A then B; A; therefore, B.”)
This fallacy is of considerable importance to historiography because it often forms the basis of models of confirmation and shows why a more sophisticated philosophical apparatus is required. A typical statement might be: “if our model/explanation of x [some event, say] is correct, we would expect to find y [some evidence, records or traces, for instance], as indeed we do.” Thus an account of some historical episode predicts that certain evidence of it will be found, and when this happens the account is confirmed or demonstrated to be correct. However, in this form the account is straightforwardly fallacious as an example of affirming the consequent.
For example, if Einstein were an extraterrestrial of superior intelligence, he should have made incredible intellectual achievements. He did, and therefore he was an extraterrestrial. We can attempt to undercut this objection by arguing that actually the evidence only makes the account more likely, but this requires further elaboration before it becomes philosophically tenable, for example by comparing different hypotheses with different prior probabilities (see Tucker 2004, for an example of a Bayesian approach that avoids this difficulty).
Bayes? Yes, historians use Bayes.
I’ve been trying to think through some other examples. Here are a few. Two political ones to start followed by some biblical ones, including some mythicist examples.
Trump Derangement Syndrome
P1: If people have a Trump Derangement Syndrome then they will criticize Trump
P2: people criticize Trump
C: therefore those critics have TDS
P1: If the Chinese Communist Party conspired to mislead the world on the coronavirus impact then the figures they released would contain anomalies
P2: The figures released by the CCP have contained anomalies
C: therefore the CCP has conspired to mislead the world on the coronavirus impact
Archaeology proves the Bible
P1: If the historical narratives in the Bible are basically true then we should find archaeological evidence pertaining to those events and persons;
P2: we find archaeological evidence pertaining to biblical accounts,
C: therefore the historical narratives in the Bible are basically true
Prophecy proves the Bible
P1: If bible prophecies were true, then we would see the events they predicted happened;
P2: we see the events prophesied did happen,
C: so the prophecies were true.
Historical evidence for the historical Jesus
P1: If Jesus existed then we would expect to find mention of him in ancient historians
P2: we find mentions of Jesus in works of ancient historians
C: therefore Jesus existed
Biblical evidence for the historical Jesus
P1: If a historical Jesus had a brother who held a leadership position in the early church then we would find some indication of that in the early documents
P2: we find a statement in Galatians that Paul met Jesus’ brother
C: therefore a historical Jesus had a brother.
Historical proof for the historical Jesus
P1: If Jesus were a most astonishingly extraordinary historical person who challenged Jewish traditions then we should see devotion to him even at the expense of Jewish traditions
P2: we see worship of him even at the expense of Jewish traditions
C: therefore Jesus was a most astonishingly extraordinary historical person . . . .
Criterion of embarrassment
P1: If the baptism and crucifixion of Jesus were embarrassing events but very well known and unable to be denied then they would be described in some form in the earliest records
P2: The baptism and crucifixion of Jesus are described in the earliest records
C: therefore the baptism and crucifixion of Jesus were embarrassing events but very well known and unable to be denied
A mythicist fallacy
P1: If Jesus were a myth then we would find the gospels full of myths
P2: the gospels are full of mythical tales
C: therefore Jesus is a myth
P1: If Christianity originated as a form of astral worship then we would be able to discern astral allusions and motifs in the gospels
P2: we can see astral allusions and motifs in the gospels
C: therefore Christianity originated as a form of astral worship
Others? Feel free to add some. My brain needs a break.
Newall, Paul. “Logical Fallacies of Historians.” A Companion to the Philosophy of History and Historiography, edited by Aviezer Tucker and Mary Kane, Wiley-Blackwell, 2009, pp. 262–73.
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