Motte-and-bailey fallacy

Philosopher Nicholas Shackel, who coined the term,[1] prefers to speak of a motte-and-bailey doctrine instead of a fallacy.[3] In 2005, Shackel described the reference to medieval castle defense like this:[2]

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. ... 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.

Shackel's original impetus was to criticize what he considered duplicitous processes of argumentation in works of academics such as Michel Foucault, David Bloor, Jean-Francois Lyotard, Richard Rorty, and Berger and Luckmann, and in postmodernist discourses in general.[2][4]

The motte-and-bailey concept was popularized on the blog Slate Star Codex in 2014.[4]

An example given by Shackel is the statement "morality is socially constructed". In this example, the motte is that our beliefs about right and wrong are socially constructed, while the bailey is that there is no such thing as right and wrong.[3]

According to Shackel, David Bloor's strong programme for the sociology of scientific knowledge made use of a motte-and-bailey doctrine when trying to defend his conception of knowledge as "whatever people take to be knowledge" without distinguishing between beliefs which are widely accepted but contrary to reality and beliefs which correspond to reality. In this instance, the easily defensible motte would be the idea that what we call knowledge is what is commonly accepted as such, but the prized bailey would be that scientific knowledge is no different from other widely accepted beliefs, the implication being that truth and reality play no role in gaining scientific knowledge.[2]

Motte-and-bailey fallacies can also be observed in informal, non-academic discussions. For instance:

• Person A: "I don't understand why people believe in astrology, there's no scientific evidence to support it."

• Person B: "The moon has enough pull to cause tides every day on Earth, but it has no effect on people? Are you trying to say humans are literal gods unaffected by nature? I guess evolution isn't real, either!"

Here, Person B has substituted an easy-to-defend motte:

• "Human beings are affected by natural forces, including the Moon's gravity."

for a controversial bailey claim:

• "Astrology's use of the positions of celestial bodies in the sky to make predictions about people's personality, characteristics, and behavior is scientifically valid."

Most astronomical objects such as stars and planets are too small, far away, or both to have strong direct gravitational influence on humans. Also, the apparent proximity of stars in a particular constellation of the zodiac is an artifact of perspective: for instance, the stars in the constellation Cancer range from 40 to 550 light-years away. Therefore, the predictions of astrology are inherently supernatural, not explainable by science.

The fallacy has been described as an instance of equivocation, more specifically concept-swapping, which is the substitution of one concept for another without the audience realizing.[5]

In Shackel's original article, he alleged that Michel Foucault employed "arbitrary redefinition"[2] of elementary but inherently equivocal terms such as "truth" and "power" in order to create the illusion of "giving a profound but subtle analysis of a taken for granted concept".[2] Shackel labeled this type of strategic rhetorical conflation of the broad colloquial understanding of a term with a technical, artificially stipulated one as "Humpty Dumptying", in reference to an exchange in Through The Looking-Glass.[2] In Shackel's description, a motte-and-bailey doctrine relies on overawing outsiders with pseudo-profundity,[2] similarly to what Daniel Dennett called a deepity.[3]

Unlike normal examples of equivocation where one exploits already existing, perhaps quite subtle, differences of meaning, Humpty Dumptying is hardly subtle. The differences in meaning are so obvious that equivocating by use of them cannot normally be pursued without first softening up the audience. The softening up is effected by convincing the audience that the dual meaning is somehow an exposition of a profundity. ... the strategy is, as in Foucault's "Truth and power", to first make use of the word in its redefined sense, then present the redefinition as if it had already been established as the deeper content of the concept. Finally, the impression of profundity is sealed by passages which elide both meanings at once.[2]

Responding to Shackel's use of the motte-and-bailey concept, professor of rhetoric Randy Allen Harris objected to what he saw as Shackel's use of the concept to gratuitously violate the principle of charity by distorting other people's arguments and failing to understand the other's position beyond what is required to attack it; Harris wrote:[6]

we are obliged to penetrate the discourse, not simply throw bricks at it. Professor Shackel shows signs of penetrating it on occasion, but consistently retreats a safe distance to just throw bricks. He accuses postmodernists of withdrawing to their Mottes rather than hoisting their battle axes to fight it out on the Bailey, but he is just as guilty of avoiding a true fight, systematically retreating to his siege engine, or whatever the offensive corollary of the defensive Motte is.

• Anadale, Christopher (10 June 2019). The Motte & Bailey Fallacy (Lecture) (video). YouTube. Retrieved 19 June 2020.