I once attended some training that discussed communication skills and one of the things they asked us was: when talking to someone, are you listening to what they are saying or are you merely waiting for your chance to talk?
For me, I know I've listened when I can make their argument for them. This also has the important point of testing what I believe in an honest way and allows for modifying of what I believe or solidifying it with better ways to explain it to others.
Sadly, many people are in the "chance to talk" side with a rather large sprinkling of "people who disagree with them never get to talk".
I have to admit to frequently doing the latter.