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.
Double-standard hypocrisy: If he applies the tricks readily to your arguments but not to his, there's a good chance he's just out to win.
Moral absolutism: If he acts as though there are absolute recipes for bringing about success and as though he has them and you don't, chances are good he's just out to win.
Moral policing: If he treats you as someone who can't be trusted, someone who he has to police because you are inherently more slippery than he is, chances are he's just out to win.
Vested interest: If winning his arguments benefit him directly, chances are good he's just out to win.
No empathy: If he can't make your argument compellingly, but can only make his, chances are he's just out to win.
There are exceptions to all of these. Deciding who is power grabbing is an art not a science. But in some cases it's much safer to bet they're just out to win in which case arguing substantive points is generally a distraction and a liability. It's not about substance; it's about power.