I’m going to assume that you disagree with their opinion in this example, because if you agreed, all you would need to say is, “I agree with your opinion,” and consider the schooling complete.
If you want to have an argument, they are giving you a gift. Most of the time, you cannot argue with a belief effectively, but you can argue with facts all day.
Do not immediately invoke google. That’s just rude and can aggravate a small argument into a much bigger war.
Instead, first ask yourself if you want to argue about it. Do you need to be right about the capital of Antarctica more than you need to have a peaceful visit with your friend? Do you want to stay friends? Do you want to stay friends with a person who insists that there’s a capital, as if the penguins would even let us know about it?
Fine, then. Assuming you want to wade into this sticky territory and want to remain friends with this doofus, tread lightly. Learning that you are wrong is painful. For some people the pain is so unbearable, they will contort words into the worst poetry weapons imaginable. Stay calm.
Begin by listening to their ideas. Imagine that you are going with them on a little thought journey. Let them know you are in their boat by finding some simple point of fact or terminology that you can agree with, such as, “Antarctica is a very interesting continent.”
Ask questions to make sure you understand what they are talking about. You may find that you misunderstood them or they misunderstood an idea that you have a bit more expertise in. “Do you think that every place has to have a capital?” you might ask. “What would be the capital of the moon?” If they have chosen a capital of the moon, it may be a lost cause. “Why would there be a capital where there are no lifeforms?” you might ask if you’re stubborn.
Remember, winning is not your mission here. You are a truth farmer in an alien territory. The ground may not accept your tilling or your seeds, but the effort is always worthwhile.
It may be a long time later that your friend says something about how the moon doesn’t need a political hub. When that happens, your most important task is not to gloat.
There’s no room for gloat in this boat.