The “Transcendental Argument for God” (TAG) is typically understood as resting upon the “Impossibility of the Contrary.” We may be in a better position apologetically if we think about the Impossibility of the Contrary (IoC) in terms of three aspects of the IoC. These three aspects of the IoC are definition, dogma, and demonstration.
What is the IoC?
“Impossibility” refers to the impossibility of predication upon the presuppositions of some position. We might also take the impossibility in view to refer to the impossibility of the truth of some position, the impossibility of the rationality of some position, the logical impossibility of some position, and so on.
“Contrary” is an informal reference to the “contradictory.” * Contradictory statements cannot both be false at the same time and in the same respect. Hence if a position is false, then its contradictory is true. Or, if a position is true, then its contradictory is false.
When the IoC is defined within the context of the Christian worldview it simply states something to the effect of, “Christianity is true and every other position is false.” Or we might say (even derivatively), “Christianity is rational and every other position is irrational.” And so on and so forth…
Obviously then other worldviews may make claims to their own versions of the IoC. The Christian, however, must always make his apologetic argument along the lines of some form of the IoC. The Christian must do so because Scripture both prescribes and describes this method. Scripture both explicitly and implicitly argues in this manner. To fail to argue using some form of the IoC is to fail to remain consistent with one’s Christian presuppositions and hence to sin. Such failure is indicative of a would-be adoption of the pretended neutrality propagated by many unbelievers and inconsistent Christians alike.
Why believe the IoC?
The reason the Christian adheres to the IoC as explained above is because it has been revealed to us. Christianity is true, and it follows, given the categories of thought provided by Scripture itself, that every other position is necessarily false. Hence the Christian believes in the IoC because God has revealed Christianity to us as true. Additionally, the IoC is taught in Scripture. For example, God claims, “I am the first and I am the last; besides me there is no god. Who is like me? Let him proclaim it. Let him declare and set it before me, since I appointed an ancient people. Let them declare what is to come, and what will happen. Fear not, nor be afraid; have I not told you from of old and declared it? And you are my witnesses! Is there a God besides me? There is no Rock; I know not any.” Isaiah 44:6-8 (ESV) God knows everything. If there is another god, then God would know that there is another god. God does not know that there is another god, therefore there is not another god. In this sense then it is logically impossible that another god exists. There is only one true God, and He is the God of Christian Scripture. It follows that positions which posit some other god are false, or in this case, impossible.
Or consider the claim made concerning, “Christ, in whom are hidden all the treasures of wisdom and knowledge.” Colossians 2:2-3 (ESV) If all of the treasures of wisdom and knowledge are hidden in Christ, then outside of Christ there are no treasures of wisdom and knowledge. All of the treasures of wisdom and knowledge are hidden in Christ. The Christian must affirm this upon the basis of Scripture. Therefore, outside of Christ there are no treasures of wisdom and knowledge. Wisdom and knowledge are impossible on the contradictory position.
Thus Scripture teaches the IoC both implicitly and explicitly and it should be affirmed by believers. We know the IoC because God has revealed it to us in His word.
How do we show the IoC?
The IoC is used in apologetic argumentation through internal critique. The apologist places himself upon the presuppositions of the non-Christian position and attempts to reason consistently with respect to those presuppositions. (Indeed, more consistently than the unbeliever who holds those presuppositions!) The position of the unbeliever is reduced to absurdity or exposed as arbitrary, inconsistent, irrational, and incapable of rendering human experience intelligible in light of its failures with respect to predication. General principles and operative features affirmed by the unbeliever are left unaccounted for within the context of the anti-Christian worldview.
None of what has been stated here is exact, nor is any of it new. We can, however, use this basic outline to begin to think through the various aspects of the IoC in order to clarify and express our position in a sound and persuasive manner. The implications of thinking about the IoC in this way will become apparent when it is applied to various apologetic encounters and popular objections to presuppositional (Covenantal) apologetics in general and TAG in particular.
* A friend wrote to express his concern about this statement. I am no longer persuaded that the puzzling use of “contrary” as opposed to “contradictory” is as easily fixed as what I make it out to be here, and I plan to do further research.