Arguments that are true by definition, so that they can be proven by reason alone without any involvement of reality. The opposite of “a posteriori”, which is arguments that are considered true because of the evidence for them being true. An example of an a priori claim that most people can (and in the opinion of this author, should) agree with is that the universe exists, rather than being a dream or illusion. An a priori argument that a vast majority of humanity disagree with is the specific claim that “X is always right, therefore any evidence against X is inherently false”, with X being any one particular person, organization, religious scripture, political doctrine or similar. Generally speaking, it s advisable to keep one's a priori beliefs as simple and basic as possible.