A logical problem is usually formulated by specifying a premise statement and a relational statement, then deriving a solution from them. In arguments used to prove or disprove the existence of God this order is often reversed. The arguer assumes the existence or non-existence of God, then formulates the premise and relational statements in conformity with that assumption. This invalid logic, which begins with the solution statement and works its way backwards, can be called "reverse logic." Reverse logic is most often seen among religious believers, though atheists also commit this fallacy because of the inherent logical difficulties in conventional notions of God.
ESSENTIALS OF LOGIC
The word logic is derived from logos, which means reason. Deductive logic is used to seek a rational solution from the known premise (initial and boundary conditions) of a given problem through a relational algorithm that forms a linking bridge between premise and the solution of the problem. Deductive logic is not so much concerned with the truth of its inference (solution) as it is with the validity of argument. (1) It differs from inductive logic, which extrapolates information beyond the premises at hand using previous history or the empirical database of a given phenomenon.
Deductive logic employs syllogism, a method originally developed by Aristotle. A syllogism consists of three statements or sets of statements. The first statement, or premise, may be a single statement or a set of statements describing what is known about the problem or phenomenon under consideration. The second, or middle, term--the relational algorithm--defines the relationship that exists between the premise and the solution. The third term is the solution, an inference that follows logically from the first two terms, in a complex problem there may be several premise statements and several intermediate solutions that ultimately lead to the final solution, if a given premise and relational algorithm are true, the solution must then also be true.
It is seldom that the solution is known beforehand. If it were, there would be no need for using the syllogism method; in other words, in such a case the application of this method would be trivial in itself.
REVERSE LOGIC AND GOD
In the arguments generally used to prove or disprove the existence of God, syllogisms are usually formulated in reverse order: the desired solution is presumed. Consider Aquinas, who went back to Augustine for his most basic interpretative principle: The truth of Scripture is inviolable. (2)
Theists who develop arguments for the existence of God believe unequivocally that God exists. Their faith tells them that God exists; for them this is irrefutable fact. Thus they begin with the third term, whose import is already "known" to them, and concoct the first and the middle terms. That is the primary reason why, as a class, deductive arguments for the existence of God do not "hang together" logically speaking. …