Why your phone makes up your words

The autocorrect function can create some real howlers. Here's how Google intends it to work.

If you type “kofee” into a search box, Google would like to save a few milliseconds by guessing whether you’ve misspelled the caffeinated beverage or the former United Nations secretary-general. It uses a probabilistic algorithm with roots in work done at AT&T Bell Laboratories in the early 1990s. 

The probabilities are based on a “noisy channel” model, a fundamental concept of information theory. The model envisions a message source — an idealized user with clear intentions — passing through a noisy channel that introduces typos by omitting letters, reversing letters or inserting letters. 

“We’re trying to find the most likely intended word, given the word that we see,” Mr. Paskin says. “Coffee” is a fairly common word, so with the vast corpus of text the algorithm can assign it a far higher probability than “Kofi.” On the other hand, the data show that spelling “coffee” with a K is a relatively low-probability error. The algorithm combines these probabilities. 

I guess if you try to tweet that you're having coffee with Kofi Anan you're in real trouble.