Motte-and-bailey fallacy


The motte-and-bailey fallacy is a form of argument and an informal fallacy where an arguer conflates two positions which share similarities, one modest and easy to defend and one much more controversial. The arguer advances the controversial position, but when challenged, they insist that they are only advancing the more modest position. Upon retreating to the motte, the arguer can claim that the bailey has not been refuted or that the critic is unreasonable.

History

Philosopher Nicholas Shackel, who coined the term, prefers to speak of a motte-and-bailey doctrine instead of a fallacy. In 2005, Shackel described the reference to medieval castle defense like this:
Shackel's original impetus was to criticize duplicitous processes of argumentation he found 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.
The motte-and-bailey concept was popularized on the blog Slate Star Codex in 2014.

Examples

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.
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.

Related concepts

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.
According to Shackel, a motte-and-bailey doctrine may rely on the appearance of profundity, similarly to what Daniel Dennett called a deepity.

Criticism

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: