Go ahead, picture a religious Jew.

Now picture a Muslim cleric.

Now an Amish farmer.

What do they have in common? Beards. And not neatly trimmed beards, but, in the popular stereotype, long, unruly beards, which connote piety, spiritual intensity and a life so hard at study that there is no time for a shave. The scholar, the mystic, the terrorist, the holy man — they all have beards.

Last month, the connection between hirsuteness and religiosity appeared in federal court, not for the first time. In this latest case, a federal court refused to consider the appeal of a Jewish prisoner in New Hampshire who had bristled against regulations limiting his beard to a quarter-inch.

In upholding a 2010 summary judgment against the prisoner, Albert Kuperman, convicted in 2002 of sexually molesting a minor, the First Circuit panel did not disagree that Mr. Kuperman had a religious obligation to refrain from shaving. But it concluded, in a decision issued July 14, that “alternative means remained open for Kuperman to exercise the constitutionally protected right at issue.” The prison, in other words, had to allow Mr. Kuperman, who has since been released, some avenue for religious observance, but not every avenue.

Being bearded is just one of many obligations that some strictly religious Jewish men uphold. Only one of the Torah’s 613 commandments applies to facial hair, and scholars disagree on the commandment’s interpretation.

But the beard is integral to many men’s religious identities, not just religious Jews’. The beard, especially the really big beard, constitutes a look, one that dictates how they are perceived by the world.

“Do not cut the hair at the sides of your head or clip off the edges of your beard,” according to Leviticus 19:27. That commandment has produced reams of rabbinic commentary. Some traditional Jews believe only the chin must remain unshaven. Others argue the unshaven area is larger, and some teachings hold that the prohibition against shaving extends to the neck. Rabbis draw distinctions between shaving (forbidden) and practices like cutting the hair with scissors, plucking it with tweezers and removing it with depilatories (depending on whom you ask, possibly permitted).

But to focus on the legalisms misses the point. In many religious communities, the beard is the man’s ID badge, his sign of membership. Like the Hasid’s black hat or the Muslim’s kufi, it’s what he acquires when he joins the community, and it’s what he gets rid of when he leaves. It is a form of religious garb, with different versions in different religious tribes.

According to Steven D. Reschly, who teaches history at Truman State University in Missouri, Amish men’s beards, without mustaches, are not religiously commanded. Their only ritual function is to distinguish married men, who wear beards, from single men, who do not. (The Amish do not wear wedding rings.) They are mainly a tradition, around which legends sprout like whiskers.

“The standard story is that the Amish do not wear mustaches or buttons because mustaches and brass buttons were associated with the French military in the 18th century,” Dr. Reschly wrote in an e-mail. “Amish men will sometimes tell you that they think Amish women got rid of the mustaches on their men because they did not like to kiss their husbands with all that hair on the upper lip.”

The beards, which, according to Dr. Reschly, “reflect late 17th- and early 18th-century rural clothing and grooming patterns in northwestern Switzerland and northeastern France,” honor the past and its folkways.

“They indicate respect for tradition, refusal to recognize changing fashions, and in general nonconformity to the world, all of which do have spiritual significance in the Amish world view,” Dr. Reschly wrote.

The beard has a long history in the Islamic world, but as with the Amish, the tradition is not commanded by Scripture. Rather, it seems to originate in a hadith, or saying, from the prophet Muhammad.

“There is nothing specific in the Koran that tells people to wear beards,” said Adnan Zulfiqar, the Muslim spiritual adviser at the University of Pennsylvania. “Mainly it derives from prophetic traditions, particularly one in which a non-Muslim delegation came to the prophet, and he was taken aback by their appearance, and he made this statement that you leave your beard but trim your mustaches.”

Mr. Zulfiqar said clerics disagreed on whether the beard was obligatory for Muslim men. “The more conservative you are, the more likely to see it as obligatory.” Those who would require the beard disagree over how long it should be, he said.

But all over the Muslim world, the full beard has come to connote piety and spiritual fervor. It is such a powerful cultural signifier, in fact, that it inspires non-Muslims, too.

“We have the Muslim beard, known as the ‘Sunni beard’ here in Philadelphia,” Mr. Zulfiqar said. “The iteration,” he added, “is pretty long and scraggly, and it has become part of the fashion here. In urban Philadelphia, you will see ‘Sunni beards’ being worn by non-Muslims as well. It’s become part of urban culture, particularly among African-Americans. They wear really scraggly, unkempt beards, and it is considered aesthetically pleasing and fashionable. And you don’t have to be Muslim.”

Of course, the beard is only a sign of righteousness. It is no guarantor, as Mr. Zulfiqar reminds us:

“I recall one gentleman who came back from a trip to Pakistan and remarked to me, ‘I learned one thing: the longer the beard, the bigger the crook.’ His anticipation was people with big beards would be really honest, but he kept meeting people lying to him.”

By MARK OPPENHEIMER, Published: August 6, 2011,