In my own life—partly real and partly virtual—and in my observation of what passes for discourse in modern culture, I find myself thinking about the difference between debate and discussion. This is largely because, while I was trained and care to discuss, most people want to debate.
It seems to me that there is a lot of truth—and a lot of Aristotelianism and Thomism—in the notion that any activity is defined partly and largely by the good or end at which it aims. For instance, the difference between a marriage and a fling is in part defined by what the two are for.
Debate, it seems to me, aims primarily at winning. Winning might be defined in different ways: in an Oxford-style debate, it is defined by net change in opinion in an audience; in a political debate, it is decided by pundits and pollsters and ultimately voters; in a forensics debate, it is determined by judges. Of course, related to winning in this sense is convincing—or exhibiting convincingness—but this sort of convincing takes it as a given that the debaters will not themselves be swayed. Like Luther, they stand where they are and can do no other.
Discussion, on the other hand, seems to aim at truth. Of course, truth is an abstract thing to be aiming at. But in a genuine discussion—a dialectic, even—the parties are aiming to get to some best view. And, it is inherent in this pursuit that each recognizes that he may not already have the truth himself, that his discussion partner may have some of it or even all of it on her side. Discussion, that is, relies on a recognition of one's own fallibility in a way that discussion doesn't, but this also means that discussion has the possibility of moving both parties to somewhere new. And, that somewhere new might even be knowledge. Debate won't take one there.
We live in a society of debate it seems, where convincing is king, as it was for the sophists. It's a shame we've given up on discussion.