Passover arrives next week, and so I have been thinking about haggadot—the book that contains the service, prayers, and songs used to celebrate the exodus of the Jews from slavery in Egypt and to celebrate and hope for freedom everywhere.

There are countless haggadot—customized for every level of observance, every political opinion, every country of origin, and every age. They’re often richly illustrated works of art, as well as orders of service. My kids’ favorite haggadah is filled with very silly cartoons.

But the haggadah that I’m most intrigued by at the moment is the Birds’ Head Haggadah. This book is famous not only for its age and its rarity—dating from around 1300, it is the oldest surviving illuminated Ashkenazi manuscript. It is famous for its amazing illustrations

Through the book, illustrations record all the important parts of preparing for and celebrating Passover—the making of matzah, the telling of the story of the Exodus, and so on. But in every illustration, the Jewish figures are depicted with birds’ heads.

Suddenly, this 14th century manuscript looks as odd as my daughters’ comic book haggadah, and reminds medieval art fans of the works of Hieronymous Bosch.

What could possibly be going on here?

Many medieval rabbis felt it was a violation of Torah to create realistic depictions of human figures. The illustrators of the Birds’ Head Haggadah, like other observant Jews before them, put bird heads on human figures in order to engage in creative expression while following the rules of their community. The result is the quirky, engaging, and deceptively “modern” feel of the work they created.

I’ve always been interested in the ways in which the rules that an artist decides to follow and the limits that artists set for themselves—whether as a matter of faith, or of style—can help to spur creative work.

It makes me think of the Law Merchant described by Paul Milgrom, Douglass North, and Barry Weingast in their paper “The Role of Institutions in the Revival of Trade”(1990). They point out that in the middle ages, “without the benefit of state enforcement of contracts or an established body of commercial law, merchants evolved their own private code of laws (the Law Merchant) with disputes adjudicated by a judge who might be a local official or a private merchant.”

As a result of those sets of laws, created by a small community for the needs of that small community, medieval trade was able to flourish and grow in rich and surprising ways. Similarly, the traditional and often restrictive rules that governed the artists who created the Birds’ Head Haggadah opened the door for a book that follows all those rules, but does so with a whimsy that communicates across the centuries.