• Dyalogues are between exactly two people. Unlike open threaded discussions, where anyone can pipe into a discussion, a dyalogue is a back-and-forth interchange between just two people. Other people can leave comments at the end, but they can not participate in the dyalogue itself.
• Dyalogues can not be easily derailed. Because there are only two people participating, a third person (or fourth, or twenty-eighth) can’t step into a healthy exchange and interrupt it, force it off onto a tangent, or otherwise disrupt the two-way exchange.
• Dyalogues don’t have a “mob mentality”. Because the focus and ownership of a dyalogue is with the two participants only, a mob of sympathizers of one of the participants can not ridicule, harrass or ignore the participants. (They can try to do so in the comments, but that section has little power to sway the dyalogue itself)
• Dyalogues are easy to follow. Try to follow an interchange between two people in a threaded discussion forum. They do happen, usually using ever-increasing quotes and “@ user” intros, but usually they’re difficult to read clearly.

This is not to say threaded discussions suck. They’re awesome. They allow the sort of round-table, group discussion that’s almost impossible in the real world. But if you’re trying to engage deeply with one person in particular, you are probably better served taking your discussion into a dyalogue instead.