From Wikipedia: “The motte-and-bailey fallacy** (named after the motte-and-bailey castle) is a form of argument and an informal fallacy where an arguer conflates two positions with similar properties, one modest and easy to defend (the “motte”) and one much more controversial (the “bailey”).”
It occurs to me that the entire Darwinian project is often portrayed in terms of a motte-and-bailey fallacy. How many times have you heard the statement “evolution is as certain as gravity”? Well, given a certain sense of the word “evolution,” the statement is true or nearly so.
Consider the following proposition: Evolution means “change in the biosphere over time.” No one – from the most ardent materialist atheist to the most fervid young earth creationist – disagrees with that statement. It is entirely uncontroversial and supported by overwhelming evidence.
Now consider this proposition: The mechanism of evolutionary change is completely explained by gradualism as proposed in the Neo-Darwinian Synthesis. That statement is controversial even among mainstream materialist evolutionary biologists.
Not only is the second proposition controversial, but also every biologist who knows the first thing about his field knows that to the case. Therefore, when a biologist makes the “well established as gravity” statement in support of Darwinism, we can know with near absolute certainty that he is employing the motte-and-bailey fallacy. The “bailey” is the highly controversial position that the Neo-Darwinian mechanism is sufficient to explain the history of evolution. When called on it, the proponent can retreat to the “motte,” which is the universally agreed proposition that the biosphere is different now than it was in the past.
We need to do a better job of calling out the motte-and-bailey tactic when we see it employed.
**Philosopher Nicholas Shackel coined the term in this paper. Excerpt:
A Motte and Bailey castle is a medieval system of defence in which a stone tower on a mound (the Motte) is surrounded by an area of land (the Bailey) which in turn is encompassed by some sort of a barrier such as a ditch. Being dark and dank, the Motte is not a habitation of choice. The only reason for its existence is the desirability of the Bailey, which the combination of the Motte and ditch makes relatively easy to retain despite attack by marauders. When only lightly pressed, the ditch makes small numbers of attackers easy to defeat as they struggle across it: when heavily pressed the ditch is not defensible and so neither is the Bailey. Rather one retreats to the insalubrious but defensible, perhaps impregnable, Motte. Eventually the marauders give up, when one is well placed to reoccupy desirable land. For my purposes the desirable but only lightly defensible territory of the Motte and Bailey castle, that is to say, the Bailey, represents a philosophical doctrine or position with similar properties: desirable to its proponent but only lightly defensible. The Motte is the defensible but undesired position to which one retreats when hard pressed. I think it is evident that Troll’s Truisms have the Motte and Bailey property, since the exciting falsehoods constitute the desired but indefensible region within the ditch whilst the trivial truth constitutes the defensible but dank Motte to which one may retreat when pressed.