Or read to yourself, and have a computer know exactly what you're thinking? If the scientists at NASA have anything to say about it, you might be able to, someday.
Here's how it works. When you talk to yourself, or read to yourself, even if you don't say a thing, your brain sends signals to your tongue and voicebox. Those signals can be picked up by sensors taped to your throat, and a specialized computer translates those signals into words.
Translating "silent speech" could be used for lots of things. Like, making private phone calls on a crowded bus, or communicating with a stroke victim who is physically unable to talk. It could even help astronauts, who find it hard to talk because of constant pressure changes. Or to help them land on Mars after their muscles have atrophied after years of space travel. The voice "translation" program could even help disabled folks surf the Internet   even without a keyboard.
It'll take a few years before this gets past the experimental stage, but the research is promising. And I'll be sure to keep you posted.