When the British theologian and philosopher Thomas Bayes died in April 1761, he left behind several unfinished papers. One of them, entitled An Essay Towards Solving a Problem in the Doctrine of Chance, reached the Royal Society two years later through the efforts of Richard Price, a friend even less well known than its author.
In this paper, Thomas Bayes turns Blaise Pascal's approach on its head. The 17th-century French scholar had begun his "geometry of chance" by studying the probability of an effect given a cause. In other words, if I gamble at a casino, what are my chances of winning?
The British mathematician reverses the question and proposes a formula for calculating the probability of a cause given its effect. In other words, if I draw three aces in poker, what is the probability that the deck is rigged and contains five aces?
The lawn is wet --------------------
The link to the digital economy is clear. If someone orders a book from an online retailer, it may be because the site's algorithm suggested it. But perhaps they read about it in the newspaper, heard about it from a friend, want to give it as a gift... or even ordered it by mistake!