Thursday, June 11, 2015

Parsons on presuppositionalism

Over at the Secular Outpost, Keith Parsons has some observations about transcendental theism:

Keith Parsons It seems to me that the CP project is like Descartes's in Meditations on First Philosophy. You raise the specter of total skepticism and seek a secure foundation for knowledge. By the end of Meditation II, Descartes only knows three things for sure--that he exist, that he is a thinking thing, and that whatever he perceives "clearly and distinctly" must be so. To safeguard knowledge from the Evil Demon, Descartes must prove that a good God exists, and this he sets out (fallaciously) to do in Meditation III.
The difference between the CPer and Descartes is that the latter seeks to prove God's existence, while the former presupposes it. However, some knowledge is required even to coherently presuppose. The Christian God must be assumed to be the sort of being that values truth and rationality. CPers therefore have to trust that their assumptions about the putative nature of the Christian God are (a) intelligible, and (b) true. Any attempt to demonstrate the intelligibility or truth of their assumption could not rest on that assumption, upon pain of circularity. Hence, any non-circular attempted demonstration of the intelligibility or truth of the assumption would violate the assumption itself by appealing to standards not validated by the Christian God.
The upshot is that we have no choice. If we want to know anything at all, at some point we have to accept the deliverances of our own reason.

The comparison with Descartes is interesting, but misses the point:

i) Descartes is questioning what we take for granted. If we systematically scrutinize what we take for granted, how much of that is indubitable? 

ii) Transcendental theism is similar, but different. The question at issue is how we can ground what we take for granted. Indeed, what we must take for granted. If we deny the existence of God, then do many of the fundamental beliefs we take for granted become groundless? Once you deny God's existence, that commits you do denying all the implicated beliefs. It's not a question of indubitable belief, but the metaphysical basis, if any, for the fundamental beliefs we take for granted. 

iii) Parsons is blending transcendental theism with a strategy to deflect the Cartesian demon. But a God who values truth and rationality is not, in the instance, the distinctive contention of transcendental theism. Rather, it's about the possibility of knowledge. What metaphysical machinery is required for truth and rationality to even exist. 

iv) You can indirectly demonstrate the necessity of the claim. You explicate the claim to demonstrate that there's no rational alternative. 

v) To counter that believers and unbelievers alike have no alternative to reliance on reason misses the point: transcendental theism doesn't deny that. The question at issue is what, if anything, undergirds that dependence. Conversely, does atheism subvert the reliability of reason? Examples include the argument from reason (C. S. Lewis, Victor Reppert) and Plantinga's evolutionary argument against naturalism. 

Sure, there's a sense in which reason is the inescapable starting-point. But an acidhead who's tripping out on LSD must still rely reason, even though his faculties are woefully impaired.  

What makes Modus Ponens valid? That is, how can we be sure that given p -> q and p, q must be true? Put more precisely, how do we know that p -> q and p jointly entail q? This is the same as asking how we know that {[(p -> q) & p] & ~q} is a contradiction. Well, we could write out a truth table showing that for every possible assignment of truth values to p and q, this expression comes out false. That is, {[(p -> q) & p] & ~q} is false on every interpretation, and this is what we mean by a contradiction. But what we get from our proof table is determined by what we put into it. We decide that every proposition has one and only one truth value, T or F, and we define the logical connectives "&" and "->" and "~" in certain rigorous ways. In other words WE make the rules that make arguments valid. There is nothing mysterious, transcendent, or supernatural about it. Achieving valid inference in logic is like achieving checkmate in chess. It often takes some cleverness to get there, but each proof, and each checkmate, is achieved in a rigorously rule-bound way.

Once again, that misses the point:

i) The question at issue isn't what makes modus ponens valid, but the ontology of logic. What are logical truths? Is modus ponens something we invent, or something we discover? Are logical truths necessary and universal? If so, what metaphysical machinery must be in place to make it so?

ii) Do we mere stipulate validity and invalidity, or must our rules correspond to modal intuitions? And must our modal intuitions correspond an ultimate and underlying reality that's independent of human cognition? 

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