What Is “The Impossibility of the Contrary”?

If one has studied Presuppositional Apologetics even a little, one would no doubt have come across the phrase “the impossibility of the contrary”. But what does it mean? Well, obviously it means that the contrary is impossible. But what is the contrary and in what sense is it impossible? And if it is impossible, what significance does that have to our apologetic approach?

Logically speaking, two propositions are said to be contraries if they cannot both be true. For example, the propositions ‘I am currently in Athens’ and ‘I am currently in Barcelona’ are contraries because they cannot both be true at the same time and in the same sense. Contraries, though, can both be false. Contradictories, on the other hand, are propositions which always have opposite truth values. In other words, A and B are contradictories if whenever A is true, B is false, and vice versa.

The phrase “impossibility of the contrary” should rather be called “impossibility of the contradictory” if we are being technically precise. Reason being that we are concerned with the position which contradicts Christian theism. The contrary, then, is the position which denies the Christian view - that is, the non-Christian worldview. 

In what sense is the contrary - the non-Christian worldview - impossible? Let’s see what Van Til had to say:

The contrary is impossible only if it is self-contradictory when operating on the basis of its own assumptions. It is this too that we should mean when we say that we are arguing ad hominem. We do not really argue ad hominem unless we show that someone's position involves self-contradiction, and there is no self-contradiction unless one's reasoning is shown to be directly contradictory of or to lead to conclusions which are contradictory of one's own assumptions.

For Van Til, the contrary is impossible because if it were to be held consistently, one would end up in self-contradiction. What Van Til describes above has been termed performative inconsistency. Performative inconsistency, simply speaking, occurs when one must deny a view in order to affirm it. And it is the fact that the contrary leads to inevitable performative inconsistency that makes it impossible.

The notion of impossibility employed here, then, can be called transcendental impossibility. The contrary is transcendentally impossible because it leads to performative inconsistency. If one denies the Christian view, one must affirm it whenever they engage in any rational activity. This is because Christianity is transcendentally necessary. 

The significance of the impossibility of the contrary to our apologetic endeavors is that demonstrating the impossibility of the contrary demonstrates the rational necessity of Christian theism. This is the essence of the Transcendental Argument for Christian Theism. 

To demonstrate the impossibility of the contrary, we must show that a rejection of fundamental tenets of the Reformed Christian worldview leads to a rejection of certain preconditions of rational experience - and , therefore, to performative inconsistency. 

Fortunately, that is a task I took on in my book, The Folly of Unbelief. In it, I go over various ways in which the rejection of Christianity leads one to philosophical and intellectual absurdity. You can grab a copy here

Cheers!

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