These are assumptions that already have it's conclusion beforehand. The very common example of this is "
Absence of evidence is not evidence of absence. If you are an atheist, why you do affirm that God does not exist?". I encountered this early on in my life in high school when a professor uttered this formulation: "you cannot deny something which does not exist". So, at first glance; seems my unbelief is unjustified and in fact, I held on to this formulation as basis for believing in a god.
However, this is a very good example of a priori assumptions meaning that the existence of a god is already assumed when it should be the other way around: assume first a neutral stance, a god does or does not exist. Then, you go about proving your deity's existence.
Let's use this analogy:
Suppose you want to discover a cure for cancer. You don't start with the assumption that there exists a cure for cancer. You start by assuming there doesn't exist a cure then you search for answers that will lead you to said cure. Imagine the laughter you'd get if you were to defend your research protocol with the a priori assumption that you already have a cure for cancer.
I post about this because I encountered this argument in the Filipino Freethinkers Facebook page. A theist, a Theology student, posted it and I had the pleasure of refuting his biological justification, he used the existence of the genetic code to argue for the existence of an intelligent god; so I had cause to jump in. And I was a bit disappointed with the refutation he gave me: original sin caused those genetic imperfections meaning because Adam and Eve did it and by extension the bible is literal. So imagine hard science facts, I used the existence of introns and exons, genetic diseases and reverse transcriptase to argue against an intelligent god, while he used Adam and Eve. Can you imagine if he was to defend a scientific thesis?
Anyway, I mention that incident because such people, theists, always cheat on their arguments. They always assume beforehand that their god exists and instead of resorting to hard facts like Science they always use long philosophical ramblings or their holy book.
So if someone wants to prove a god's existence, it's very simple: provide evidence. However, I will tell you that these things DO NOT count as evidence:
1. the bible (do you really want to go there? With your god condoning slavery, genocides, rape, misogyny and torture)
2. subjective experiences like miracles and apparitions (I mean it should be something objective meaning I, personally, can go out and check it INDEPENDENT of you. Heck, use this as evidence and I'll think there's something wrong with your pre-frontal cortex.)
And please, do not even think of shifting the burden of proof on me. The one who proposes the claim (God exists) must be the one who proves it.
