You can observe the world. I'm assuming you're not locked in a room somewhere and handed a set of first principles that you have to use to reason out what the w

You can observe the world. I'm assuming you're not locked in a room somewhere and handed a set of first principles that you have to use to reason out what the world is all about. You adopt beliefs that explain observations and successfully predict future observations. When beliefs fail to do that you abandon or refine them. It's in this process of refining beliefs that you watch out for fallacious reasoning to try to ensure that you are correctly understanding what you observed. I don't know anyone who just picks some first principles and goes from there. I agree that seems silly.