This post by Manuel Vargas at The Garden of Forking Paths is about how philosophers argue, but you don't need to be a philosopher to get the idea. The question is, How do you win an argument? There are at least four ways, but the first and most obvious may not be the best model of reality:
1) You convince your opponent by making a knockdown argument from indisputable premises.
2) You move your opponent from strong opposition to weaker opposition.
3) You convince a neutral bystander.
4) You move a neutral bystander in your direction.
It strikes me that many recent books (hello, Richard Dawkins and Daniel Dennett) suffer from not being quite sure which of these goals they're trying to achieve. (Of course I haven't mentioned goal 0, which is to hear yourself talking very loud.)
(Hat tip to Leiter Reports.)