Close your eyes and pretend you're in the gallery of an art museum. Now imagine the types of misbehavior around you that would cause a guard to intervene.

Pop quiz: Did those transgressions include a patron sketching an image of an admired artwork? On paper, in pencil?

Welcome to the strange world of the Fine Arts Museums of San Francisco, where there's a ban on sketching in special exhibitions such as the wonderful "Van Gogh, Gauguin, Cézanne and Beyond" now at the M.H. de Young Memorial Museum.

The de Young's not the only museum with such a Pecksniffian prohibition, but it's the exception rather than the rule. An exception that mocks the way that art is transmitted from one generation of believers to the next, and mocks the stature of museums within our cultural landscape.

The post-Impressionist treasures are on loan from the Musée D'Orsay, a Paris institution that, for the record, assures us on its website that "freehand pencil sketches" are allowed. But during the months the artwork resides within Golden Gate Park, "sketching, photography, videotaping, and cell-phone cameras are not allowed," according to the de Young's website.

Nor is this one of those rules that exists only in cyberspace. I wasn't packing graphite during my visit, since stick figures are as artistic as I get. But I know at least two people who were and, when they stood or sat quietly trying to render hints of the magic around them, were told not to draw in their (small) notepads.

While the de Young does allow sketching and photography in the permanent collections, the special exhibition curbs apparently have existed for years - a defensive posture that puts it in the company of the Art Institute of Chicago and the Philadelphia Museum of Art. But most institutions that I checked with have no such edict in place.

Pencils are allowed in all nooks of New York's Museum of Modern Art, for instance, and the Museum of Fine Arts in Boston only concerns itself with serious replication (as in, "you must obtain a written permit to copy using oils or acrylics, and/or to use an easel"). San Francisco Museum of Modern Art? As long as you don't use a pen, you're fine.

Heck, the Berkeley Art Museum goes so far as to have pencils available at the counter where you buy your ticket.

At the J. Paul Getty Museum in Los Angeles, Clare Kunny of the education department was surprised I even called to ask.

"This is something we highly encourage," Kunny said. "It's an age-old tradition."

Bingo.

The person who pauses at a painting like Paul Cezanne's "Gustave Geffroy" and sketches a personal response isn't guilty of copyright infringement, an absurd justification for intervention that security guards are known to use. They seek comprehension through emulation, as artists have throughout time.

This sort of person is far less of a distraction than the museum-sanctioned flocks of gallery-skimmers wearing headsets that transmit $7 "audio tours" - people who ricochet from one numbered destination to the next, waiting to be told what to see.

But the headset hordes are revenue generators, so they're allowed. The main concern with sketching in special exhibitions seems to be a pragmatic question of crowd control. Museum directors want blockbusters, galleries stuffed with ticket-buyers and once you enter the gift shop, you can't retrace your steps.

This attitude is especially galling at the de Young because it is a public, city-owned institution in a public park.

Nor is it a stony, fenced fortress: One of the many things I like about the redone de Young is the generosity of the architecture by Herzog & de Meuron and the surrounding landscape by Walter Hood. The design pulls the park into the folds of the building, drapes sculptures and play space around it; large portions of the ground floor are ticket-free, as is the observation tower.

Yes, you buy a ticket to cross certain lines. But the sense is that of a communal space where we can explore the intersections of art and society, art and self-discovery, art and personal expression.

The implicit message: We aren't just consumers or drones. Unless, of course, a special exhibition hits town. Then, you'd better hope the painting that inspires you also inspired a gift shop postcard.