Bill gates Bill Gates. Inc

Bill Gates says that he reads about fifty books a year. 

Why would the world's richest man — worth an estimated $78 billion — spend so much time leafing through pages?

Most of what he reads is nonfiction that explains something about how the world works.

His favorites from 2015 dug into how buildings are built, how children succeed, and how diseases are eradicated. 

In a recent interview with Katherine Rosman at the New York Times, Gates explained that reading has always been one of the "chief ways" that he learns. 

"These days, I also get to visit interesting places, meet with scientists, and watch a lot of lectures online," Gates explained. "But reading is still the main way that I both learn new things and test my understanding."

Sometimes, a book will help him see familiar things in a new light. 

"For example, this year I enjoyed Richard Dawkins’s 'The Magic of Reality,' which explains various scientific ideas and is aimed at teenagers," Gates writes. "Although I already understood all the concepts, Dawkins helped me think about the topics in new ways. If you can’t explain something simply, you don't really understand it."

It's fascinating that Gates, one of the greatest technologists in history, relies on one of the oldest information technologies — the written word — to further his understanding of the world.

Not even on an e-reader— the Bill and Melinda Gates Foundation head reads print. 

As the American philosopher Morimer Adler noted in "How to Read a Book," books are the best teachers available for people who aren't in school. And Gates, the world's richest man (and perhaps one of the most studious), uses reading to add to his understanding of the world. 

"This is one of the things I love about reading," Gates said. "Each book opens up new avenues of knowledge to explore."

Check out the full interview here.