Washington — It was 20 years ago today that Scott Fahlman taught the Internet how to smile.

The IBM researcher has devoted his professional life to artificial intelligence, the practice of teaching computers how to think like humans.

Mr. Fahlman is known for his work with neural networks -- a computer technique designed to mimic the human brain -- and helping develop Common Lisp, a computer language that uses symbols instead of numbers, but the bearded scientist is perhaps best known for a flash of inspiration that helped to define Internet culture, in all of its ungrammatical glory.

On Sept. 19, 1982, Mr. Fahlman typed :) in an online message.

The "smiley face" has since become a staple of online communication, allowing 12-year-old girls and corporate lawyers alike to punctuate their messages with a quick symbol that says, "hey, I'm only joking."

Mr. Fahlman's innovation has since inspired countless other "emoticons" like ;-) to signify a wink or :0 to show surprise.

"I've certainly spent 10 times as much time talking with people about it as I did coming up with it in the first place," Mr. Fahlman said from his Pittsburgh home. "Hopefully my actual research career will add up to more in the long run."

In the early 1980s, computer networks were rarely found outside university science departments and secretive government facilities.

But even then, discussions on primitive online "bulletin boards" could quickly turn nasty when touchy users misinterpreted remarks meant to be taken lightly.

After a particularly tangled joke about mercury contamination in an elevator, users of a Carnegie Mellon University bulletin board proposed a variety of markers for humorous comments, including +, %, &, (5) and --/.

Mr. Fahlman suggested :), along with the admonition to "read it sideways." Before long, other bulletin board users were placing the smiley face in their messages. The practice spread as Internet users found the symbol useful as a rough approximation of a twinkle in the eye.

Predictably, the smiley face encountered a few frowns as the online population exploded.

"Humans have managed to communicate with the written word for thousands of years without strewing crudely fashioned ideograms across their parchments. It is as if the written word were a cutting-edge technology without useful precedents," groused Neal Stephenson in the New Republic in 1993.

Mr. Fahlman stands by his creation. "If Shakespeare were tossing off a quick note complaining about the lack of employee parking spaces near the Globe Theater, he might have produced the same kind of sloppy prose that the rest of us do," Mr. Fahlman writes on his Web site.

Yahoo!, Microsoft and America Online all incorporate emoticons into their instant-messaging systems, while telecom firms, jewelry makers and online retailers have filed trademark applications for products and slogans that incorporate Mr. Fahlman's smiley face.

But Mr. Fahlman has never seen a dime from his creation.

"If it cost people a nickel to use it, nobody would have used it. This is my little gift to the world, for better or worse," he said.