It's often hard to tell whether a debate is about substance or power. And it matters. It's tacky to accuse your opponent of craving power when he's actually talking substance, and it's dangerous to discuss substance when he's just vying for power.
Since it matters, we need good ways to figure out when its about which. How can you tell when your opponent is using substantive arguments as a ploy to get power? It's a good and hard question. You can't tell. You can only guess, but some guesses are better than others. In general the symptoms of power grabbing include:
Ladder dancing: If he refuses to visit substantive issues on the scale of analysis where you think they are. If you say the problems are on the 10th rung and he flits to rungs below and rungs above, anywhere but where you are, there's a good chance he's just out to win.
Trick bagging: There's a bag of generic tricks we use to discount and dismiss each other's substantive arguments and still look reasonable. If he reaches into the bag fast and fluently in response to your challenges, there's a good chance he's just out to win.