LOTR Discussion Project: Book V, Chapter 4: The Siege of Gondor

[Gordis]

I think Denethor, as a true High Numenorean had mind-reading powers and read some Pippin's thoughts. Gandalf implied as much.

The palantiri are not the devices made for mind-reading. It is but a means of communication, like cellphone or, more precisely, like a video-conference. If users have own mind-reading powers (like Sauron) they can do that via palantiri. That is how I see it.