Once we know how to identify conventions, we’ll find them everywhere. They manifest as customs, the tacit rules of a community. Customs can be so invisible within a group that we notice them only upon encountering alternative ways of life. “There are probably young men from Nevada,” writes the journalist Calvin Trillin, “who have to be drafted and sent to an out-of-state Army camp before they realize that all laundromats are not equipped with slot machines.” We are more cognizant of conventions when they take the form of norms and manners, because we may be reluctant to follow them. Meanwhile, traditions, like lederhosen and dirndl, are conventions anchored in historical precedence that serve as explicit symbols of the community. Beliefs can also have conventional elements. This is clear for superstitions: Americans fear the number 13, while Italians believe it’s lucky.

Sumptuary laws codified which classes could wear which garments.