The freedom to be exposed to and engage in true substantive argument has been the historical strength, and even greatest gift, of a college education in the United States. Recently, that strength has been treated as a weakness by many who would rather stifle debate than brook dissent they view as offensive.

There seems to be an increasing reliance on a number of questionable debate tactics and rhetorical devices designed to silence any opposition. Examples range from the student who hurls ad hominem attacks to the post hoc-ster, deviously “conflating” correlation and causation. However, there is one especially effective phenomenon, often unchallenged in its power to shut down balanced debate, smother viewpoint diversity and wall off homogenous dogma. It can be seen in the debate about almost every important social issue.

But first, a little history. In some medieval castles, when enemies breached the first line of defense, the inhabitants would retreat from the outer courtyard (the “bailey”) to a tower on top of a mound (called the “motte”) where they could take refuge and shoot arrows at the enemy until the hostile forces gave up. After doing so, everyone would return to the more pleasant and productive bailey, secure in the knowledge that the motte would protect them if another attack were made. Mottes were safe but economically useless, and baileys were profitable but vulnerable. For best results, both were necessary.

That’s why philosopher Nicholas Shackel coined the term “motte-and-bailey” to describe the rhetorical strategy in which a debater retreats to an uncontroversial claim when challenged on a controversial one. The structure goes something like this:

First, someone makes a controversial statement from what blogger Ash Navabi calls the “courtyard of ideas.” Then when that statement, the bailey, is attacked, the speaker retreats to the motte, the place of “strict terms and/or rigorous reasoning”—falsely claiming that she was just making an obvious, uncontroversial point, one that could not possibly be challenged by any right-minded individual. Finally, when the argument has ended, she will go back to making those same controversial statements—the argumentative bailey, having successfully fended off all attackers. The point is to defend a controversial idea by systematically conflating it with a less easily-assailable one.

Psychiatrist and blogger Scott Alexander popularized the term, and noted its seeming ubiquity in public debates. To take a concrete example, consider much of the rhetoric surrounding the validity of any number of wars. Often when vehement supporters of a given war are challenged by anti-war protestors or people who generally think America spends too much on defense, they respond with the same tired motte “but don’t you support our troops?” Certainly we would agree with this uncontroversial statement; we do support our troops. However, supporting troops obviously doesn’t necessitate supporting a particular war in a particular set of circumstances. Yet, no one wants to appear to not fully support the troops, so the motte effectively silences them when they should be in the to-and-fro of the bailey. This kind of rhetorical device has been used to help justify unnecessary and expensive wars that are widely considered to be unsuccessful.

It is easy see how this tactic is applicable to nearly any argument one could make. The retreat to the motte at any sign of attack is a manipulative rhetorical trick to brand the opponent as unreasonable when in fact the opposition may not be unreasonable at all. Even more nefarious, the tactic also creates and reinforces echo chamber behavior; it allows one to easily dismiss critique without having to do the intellectual work necessary to critically examine one’s positions. By its nature, it divides people and stifles true argument.

The motte and bailey tactic is most dangerous when it stands in the way of legitimate, deliberation and debate. An argument that relies on this rhetorical ploy–that gets to avoid defending its weakest points, and obscures differences and logical links between different beliefs–is exactly what we need to avoid. As campuses become more and more philosophically homogeneous, it should be more socially acceptable to point out and criticize argumentative fallacies and spurious reasoning in classrooms, at protests, and even in day-to-day conversation, not less. In order to maintain and promote viewpoint diversity on campuses and beyond we should not shut down ideological diversity.

But even if achieving these goals proves harder than anticipated, we must still seek to elevate reason over rhetoric–the motte and bailey being an example of the latter–to have the argument rather than just tactically ending it. The virtue of the process is that people will have to critically examine their beliefs, engage with different ethical systems, and not flee information that contradicts what they hold to be true. In the end, some might change their views and some might not, but either way their beliefs will have more moral authority for having been truly earned.