_________________________________________The first point of contention with presuppositionalism is its fallacious use of presuppositions—obviously the very thing this method is named after. First, it’s difficult to even track down an unambiguous definition of presupposition in the literature. Second, the definitions and uses of the word seem to contradict each other constantly. Let’s begin our substantiation of such assertions by examining the definition of presupposition given by Greg Bahnsen in Always Ready:
Eventually all argumentation terminates in some logically primitive starting point, a view or premise held as unquestionable. Apologetics traces back to such ultimate starting points or presuppositions. In the nature of the case these presuppositions are held to be self-evidencing: they are the ultimate authority in one’s viewpoint, an authority for which no greater authorization can be given. So then, all apologetic argumentation will require such a final foundation, an ultimate and self-validating presupposition or starting point for thought and commitment. (p.72)
What Bahnsen is talking about here is, basically, that one’s epistemological foundation—whatever propositions this foundation consists of—constitutes their presuppositions. For our epistemological foundations are those ultimate starting points of reasoning and knowledge. In fact, these starting points are what Scholastics refer to as First Principles—which consist of the laws of logic et. al. It is these first principles, or presuppositions, that form the basis of knowledge and reason. That is to say, we could not reason, think, or know anything without having these presuppositions as our foundation. Subsequently, any proposition, theory, or idea will, if continually pushed upon epistemologically, inevitably terminate in our presuppositions.
So, it seems that the presuppositionalist has at least defined his core term, presupposition, in a coherent and valid way that enables us to carry on with his reasoning. Well, not so fast. While the definition above seems adequate, other statements by the presuppositionalist seem to contradict said definition:
Understanding and knowledge of the truth are the promised results when man makes God’s word his presuppositional starting point for all thinking. (p. 20)
The Christian has new commitments, new presuppositions[.] (p.17)
The unbeliever must renounce his antagonistic reasoning and embrace a new system of thought; thus his presuppositional commitments must be altered. (p. 68)
Notice that in these quotes, Bahnsen is saying something quite strange. That is, he is saying that we can alter or change our presuppositions. So, remember the foundations of reason and knowledge that we discussed above? Those starting points of epistemology of which every proposition will ultimately terminate in? Those presuppositions? Yeah those, according to Bahnsen, can be changed!
Of course we need to ask ourselves whether or not any of this makes sense. That is to ask, is it actually epistemologically possible to change our ultimate foundations and starting points of knowledge and reason? Well, quite frankly, no.
First, if presuppositions are our starting points for knowledge and reason, then we cannot simply start somewhere else; these starting points cannot simply be supplanted. Why? Well, because they are the foundations of knowledge! One cannot simply knock down the foundations of one’s knowledge since said knowledge is built on those very foundations. If the foundations go then so does any epistemic proposition ever subsequently promulgated or known.
Second, remember that said foundations are presupposed. That is to say, they are epistemologically assumed or supposed at the beginning of our reasoning. That’s the entailment of the prefix pre. That being said, one cannot simply swap a presupposition with any other proposition. A presupposition can only, by definition, stay assumed beforehand. Thus stated, at no point in our reasoning, ever, can we rearrange our starting point or foundation—that’s why it’s called our starting point.All this is to say that the presuppositionalist cannot have it both ways. If he means by presupposition, the starting point and foundation of human knowledge and reasoning, then this simply cannot be exchanged for the revelation of God—or anything else. It’s not epistemologically possible. Thus stated, we cannot arbitrarily choose to presuppose anything, much less the word of God, and therefore presuppositionalism, which states that we can and must do this, is blatantly false.