You know when there is something that you were never taught, but you know to be true, like logic? That is the method of a priori. This method basically says that there are just some things that we just naturally know. Of course, the question becomes how do you we tell what is true and what isn't. Since this knowledge is supposedly just known, there is usually not an easy way to prove this knowledge. That is this method's problem, so let's move on to the next one once again...