How did a 17th-century clergyman invent the digital economy? originally appeared on Quora, the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google Plus.

The sermons of Thomas Bayes, a nonconformist minister of Tunbridge Wells, England, were undistinguished. Bayes was so obscure that no known portrait of him exists. (The one on the Wikipedia page is probably someone else.) Even Bayes’ biography is slight. The only recorded anecdote that might be worthy of a biopic holds that Bayes once greeted three aristocratic visitors from the East Indies. Bayes showed them a marvel they had never seen: ice. Bayes informed his skeptical visitors that it was a solidified form of water, created in the cold of English winter. “No,” objected the eldest visitor. “It is the work of Art!” Bayes proved the ice was water by melting it in the fire.

Bayes drew his last breath on April 17, 1761, leaving behind something more marvelous yet: a mathematical theorem that would one day rule the digital economy.

Like many British clergymen of his time, Bayes dabbled in science and math. He came up with the result we now call Bayes’ theorem. It is this that makes possible for tech companies to monetize “personal information” collected by free apps. The data allows marketers to predict what users will buy. These Bayesian predictions, updated with every click, swipe, post, or GPS coordinate, are crucial to many business plans.

Bayes’ story is interesting because it counters so much of the common wisdom about invention. We are told that necessity is the mother of invention. But Bayes’ theorem was more like another cliché, a solution in search of a problem. No one even knows what Thomas Bayes thought his theorem was good for (hardly for helping 17-year-old influencers rake in seven-figure endorsement contracts). Some suspect that Bayes was reacting to Scottish philosopher David Hume, who ignited an 18th-century culture war by questioning the reality of Biblical miracles. As a STEM-savvy man of the cloth, Bayes must have felt himself torn between faith and the Enlightenment. With his theorem he addressed a central question of the scientific worldview: How does a rational person use new evidence to adjust his or her beliefs?

Bayes’ peers judged his theorem to be more trouble than it was worth. It took computers to unleash its full power. For that reason Bayes’ theorem found little application until the 20th century. It was adopted by the insurance industry, the military, and then technology companies.

One contemporary application is fighting spam. So-called Bayesian filters help protect your inbox from junk messages. They compare the text of e-mails against a continuously updated list of words and phrases that appear in unwanted messages (FREE, Earn $, cure baldness, Viagra, etc.) Any matches are circumstantial evidence, in that they can’t prove a message is spam. But a message having matches to the spam list is more likely to be junk than a message with no matches. Those messages exceeding a threshold are marked as spam. If you check your “junk” folder, you’ll see it works better than you may know.

Bayes’ story demonstrates that inventors don’t always know what their inventions are good for. Finding uses for inventions is a creative act in itself—and sometimes the most difficult one.

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