Sir Alexander Fleming, the Scottish bacteriologist (1881-1955), had a most peculiar pastime. He liked to paint pictures in petri dishes with a palette of living germs. Being thoroughly familiar with micro organisms --their individual colors, textures, and so forth-- he was able to produce striking portraits: a mother and child, a ballerina, his house.

Fleming is far better known for his break-through discovery of penicillin. But he was clearly a man who knew how to play. "I play with microbes," he once said of his work. "It is very pleasant to break the rules."

How sad that the rest of us have such a hard time being serious about silliness. A recent op-ed piece in the New York Times lamented the all-but-complete disappearance of suburban games of "catch." The writer's point was that the kids (and parents) seem so caught up in competitive activities of one kind or another that there's little patience left for something as aimless as tossing a ball.

Scientists, ironically, have always known the value of fooling around. Einstein was famous for his "thought experiments," fantastic flights of fancy that led him to imagine, for example, what it might be like to ride on a light beam, a cerebral magical mystery tour that offered him the insights he needed to produce the special theory of relativity.

"It is striking how many great scientists have incorporated play into their own lives and work," concludes Michigan State physiologist Robert S. Root Bernstein in a recent issue of The Sciences (from which the Fleming anecdote was taken). "One mental quality that facilitates discovery... is a willingness to goof around..."

Still, I worry about the rest of us. We're frightened of play --and perhaps for good reason. Play is out of control. Play, by definition, is a suspension of rules, an invitation to re-invent reality, to reformulate established ways of doing things. In real play, we try things just for the heck of it, just to see what happens. In other words, we take risks. What we risk, above all, is making a fool of ourselves. Some people consider this a fate worse than death. I consider it a necessary part of doing business.

Without breaking rules, it's impossible to come up with truly new solutions. Yet even giant corporations and established political parties have become so cautious that they rarely serve up anything that isn't thoroughly tested. We are focus grouped and market-researched to death. From such sterile ground no fertile product can issue --be it a prototype for a new magazine or a political platform. Even foundations and Federal agencies have become so careful (with a very few notable exceptions) that researchers must submit lengthy, detailed descrip-tions of the expected outcomes of the ex-periments or projects they wish to pursue. Ironically, this precludes the discovery of anything unexpected, which, in effect, precludes discovery itself. "Discovering" something you already know is there is like "discovering" the eggs the bunny hid on Easter morning. Nature, unfortunately, isn't so cooperative and may hide treasures in the most peculiar places. She may even decide to hide toothbrushes instead of eggs, perhaps in a fifth (or tenth) dimension.

In science, the stories of making fundamental discoveries while poking around in places we don't belong are legendary: Johannes Kepler (1571-1630) discovered the true elliptical shape of the planetary orbits after devoting a lifetime to trying to prove they had to be circles. Kepler's method was nothing more than an elaborate game of blocks --trying to fit spherical orbits into cubic (and tetrahedonal) holes.

Making mistakes isn't merely to be tolerated. It's absolutely essential. Play is the name we give to this freedom to mess around&emdash;to go out on a limb with the full knowledge that we might fall flat on our faces.

In this sense, democracy is a very playful form of government. Making mistakes is built into the system, along with the means for correcting them. We even send up "trial balloons" --the safest way to take a risk, like the child who lobs a fresh remark, then smiles as if to say, 'I didn't mean it." Play allows us the flexibility to continually tune our responses. When we "play" the wheel, or a sailor "plays the jib," we refer to adjustments too fine to rely on logic, improvements so subtle they can be guided only by intuition.

The one place we can recognize the crucial role of play is in the arts (although I suspect that this is because we do not take "creative" people quite as seriously as "scientific" types). I immediately think of the masterful way Annie Dillard, for example, takes an idea and toys with it like a cat: hands, perhaps, or the oddity that birds should sing. Perhaps it is a form of bird play. Word play. Word bird play.

Like other parents, I often abdicate the play in the house to the kids, letting them be silly for me. At times I even tell them to "stop fooling around" and "do something constructive" --although I don't know why I should. I yell at them not to put Doritos in the orange juice although I don't know why they shouldn't.

Creativity always comes from odd juxtapositions; inventions and discoveries are always based on unexpected combinations and strange connections. Yet we can't free-associate if we don't do things for no good reason.

Even when grown-ups do go out to play these days, their games seem oddly intense and rigid: handball, tennis, running (who skips anymore?), swimming laps. We no longer cheer ourselves up by buying a frivolous hat. We dress for success. Children's fashion has become serious business. We power eat. Even in video games, we compete with ourselves. There's a noticeable absence of giggles.

Years ago, I remember sitting in meetings where people would lob ideas about freely --sometimes very silly ideas. Someone might pick up a silly idea and make it sillier; sometimes we'd giggle; and sometimes someone would turn that silly idea into a brilliant one.

Recently, I've sat in too many meetings where no one would dare toss out an idea for fear it will be shot down. You can't suggest anything you aren't absolutely sure about. Someone might throw you a curve ball. Instead, we write well-researched memos. But the best ideas often don't come from memos. They come off the wall.

We're no longer the Me generation, but we may be something worse --the C-generation. C for Cautious. Perhaps it is not surprising that we walk the straight and narrow like gymnasts on balance beams, afraid of falling downward toward mobility, medical waste, nuclear holocaust. There's even a hole in the sky. Our self-help books advise us how to "swim with the sharks."

We'd be better at finding solutions if it weren't for the self-consciousness that makes us censor our best ideas, that snuffs out our brightest notions before they ever have a chance to catch fire, that prevents us from imagining options that are "obviously wrong." Play means an openness to consider the outrageous; to attempt things we'd never otherwise try; to test the limits of the systems we've developed to govern, feed, educate ourselves.

As long as we hide under the covers of conventional wisdom, we can't come up with the creative approaches so badly needed in areas such as housing, environmental protection, foreign policy. As long as we're busy looking over our shoulders to see what other people think of us, we can't really look ahead.

As long as we continue to take ourselves so seriously, we'll never find the energy or courage we need for matters that really warrant our serious attention.