Two people who each search on Google for “Egypt”...

Two people who each search on Google for “Egypt” may get significantly different results, based on their past clicks. Both Yahoo News and Google News make adjustments to their home pages for each individual visitor. And just last month, this technology began making inroads on the Web sites of newspapers like The Washington Post and The New York Times.

All of this is fairly harmless when information about consumer products is filtered into and out of your personal universe. But when personalization affects not just what you buy but how you think, different issues arise. Democracy depends on the citizen’s ability to engage with multiple viewpoints; the Internet limits such engagement when it offers up only information that reflects your already established point of view. While it’s sometimes convenient to see only what you want to see, it’s critical at other times that you see things that you don’t.

Eli Pariser, the president of the board of MoveOn.org, When the Internet Thinks It Knows You. Via the New York Times.