Decipher the most basic difference between theism and atheism.
 Define the word "God" in a way that would satisfy the minimally required difference between theism and atheism so that if one were true, the other would be false.
 Establish whether the atheist :
(A) neither believes nor disbelieves in the existence of God or
(B) whether the atheist disbelieves in God, as they cannot hold both positions simultaneously.
If the atheist is in group (A), then they don't have a stance on the issue that would require any rational justification as to whether God does or does not exist. If they had a rational justification for believing that God does not exist, then this would warrant disbelief and the atheist would not be in group (A) because in order to be in group (A) the atheist must *not disbelieve* in the existence of God. If the atheist has rationally justified grounds for believing that God does not exist, but has no rationally justified grounds for believing God DOES exist, and the atheist still considers themselves to be in group (A), then they are irrational. It is irrational to have evidence supporting disbelief and no evidence supporting belief while still neither believing nor disbelieving the in the existence of God since the most rational approach is to base your beliefs on the preponderance of the evidence.
Since the atheist in group (A) has no evidence against God's existence, any amount of evidence indicative of God's existence would rationally justify belief that theism is true and consequently, that atheism is false. In this instance, any amount of evidence would rationally justify belief in God's existence because the evidence would be net positive.
If the atheist is in group (B), they have a burden of proof to show why disbelief in God is rationally warranted. They must provide evidence against the existence of God. If the evidence against God is greater than the evidence in support of God, disbelief is rationally warranted.
 the theist must provide the evidence that supports their view, and, if the atheist is in group (B), they must also provide the evidence that supports their view too.
 depending on the preponderance of evidence provided in the previous step, this will determime whether believing the claim is rationally warranted or not, or, depending on whether the atheist in group (B) provides counter-evidence, whether disbelief is rationally warranted.