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 a...