Philosophical Dialogues
The great philosophical "dialogues" are, of course, hardly dialogues. One voice is that of the philosopher, the others are foils of varying degrees of density and compliance. Large stretches of Plato's dialogues are merely expository essays with "It is so, Socrates" (or similar) regularly tossed in. In his Dialogues Concerning Natural Religion, Hume gives his foil Cleanthes a bit more philosophy than is usual, but the crucial final two parts, XI and XII, are Philo's almost alone.
In my view, this is merely an accident of the mundane realities of writing and publishing. Nothing prevents the compelling presentation of more than one side of an issue in a dialogic format. Normally, though, this will require authors with divergent views and an ability to work co-operatively with each other. My recent experience writing in this way with Russ Hurlburt (in our recent book) has convinced me that this can be a very useful method both for the authors and for readers. There's nothing like genuinely engaging with an opponent.
The dialogue is very different from the pro and con essay with replies. The dialogue has many conversational turns; the essay and replies no more than four. The dialogue invites the reader to a vision of philosophy as collaborative and progressive, with the alternative views building on each other; the pro and con essay invites a combative vision. The dialogue is written and re-written as a whole to cast each view in its best light given what emerges at the end of the dialogue, eliminating mere confusions and accommodating changes of view.
David Lewis published a couple of genuine dialogues on holes. John Perry has published delightful introductory dialogues on personal identity and on good and evil (though Perry is summarizing existing arguments rather than developing new ones). Surely there are other good exceptions, but they are rare.
I wonder how different philosophy would be -- and better -- if the standard method were to meet one's opponents and hash out a dialogue rather than to write a standard expository essay....