Sunday, February 22, 2009

Post-blogging the Central: Plantinga and Dennett

The Central APA in Chicago this past weekend seemed fairly empty, although I heard from one of the organizers that registrations this year were about the same as last year. One of the more interesting sessions was in the very last time slot, and had Dennett commenting on Plantinga's "Science and Religion: Where the Conflict Really Lies". Partly what was remarkable about the session was how many people were there. The room was changed at the last minute to accommodate the additional interest, but even so, it was still standing room only. With at least 200 people packed into a small conference room, it was certainly one of the better attended APA events that I have been to.

I had to leave early to make my flight, so I only heard Plantinga's talk. Here I didn't hear much that was new. In the first half Plantinga argued that a committed theist could accept evolution because evolution per se is compatible with theism. This is mainly because the process of natural selection with random variation was said to be consistent with a divine plan which guided what we see as random. I am not sure how much this point of view depends on Plantinga's view that the warrant for theism is basic, but granting that point, I can see the coherence of his position.

The second half of the presentation argued that there is a quasi-religious "naturalism" which is in fact in tension with belief in evolution. Here Plantinga rehearsed his notorious argument that the combination of naturalism and evolution is self-defeating because it undermines the belief in the reliability of our cognitive faculties, and so provides a defeater for these beliefs.

Hearing the argument again drew my attention to one of the steps that seems very problematic. Plantinga's first premise is that P(R/N&E) is low. Here R is the belief that our cognitive faculties are reliable, N is naturalism and E is evolutionary theory. My concern is that even if this probability is low, that is irrelevant to the existence of defeaters. For a basic point about conditionalizing is that we should only conditionalize on our total evidence. Often this is captured by some kind of K meant to encapsulate all our background knowledge. So, even if P(R/N&E) is low, P(R/N&E&K) may be higher, and actually end up being high enough to avoid a defeater for R.

If we ignore total evidence, we can come up with easy defeaters for theism T. For example P(T/S) is low, where S is suffering. But of course theists are not forced to conditionalize on S, but can also include other beliefs from their store of background knowledge.

I am not an expert on the discussion of this argument, so maybe someone has made this objection before. Any comments are welcome, especially by those who saw the rest of the session!

Update: there is now an extended description of the session here.


Anonymous said...

Anyone? Please?

Though I wish I too could have attended, I'd also love to get a first-hand account of the whole session!

Michael Bergmann said...


Seeing the rest of the session wouldn't have helped you much in terms of your question. Plantinga deals with this question you raise (he calls it the Conditionalization Problem) in a number of places. He discusses it in section IV.C of his 1994 paper "Naturalism Defeated" (unpublished but available online here:
alspaper.htm). He also deals with it in his replies in the 2002 Beilby anthology *Naturalism Defeated* in section I.C called "The Conditionalization Problem" (and in his replies in that volume to me, Tim O'Connor, and Ric Otte). It probably comes up in the 2008 debate volume with Tooley called *Knowledge of God*, I don't remember.

Plantinga's reply isn't easy to state briefly. You point out that even if P(R/N&E) is low, P(R/N&E&K) might be higher. The problem, as Plantinga sees it, is that of determining what parts of K can be added to N&E to avoid the problems he raises. If I believe that XX is a drug that has a 90% change of causing serious unreliability in a human's belief forming mechanisms and I then come to believe that I've just ingested XX, it looks like I've got a defeater for R for me. Let X = the proposition that I've just ingested XX. I now believe X and P(R/X) is low (where R is specified to me). What can I add to X to avoid this problem? Well, at the moment I believe R. Could I just add *that* to X so that I get "P(R/X&R) is high" and thereby avoid the problem? It seems not. But then what could I add? And under what conditions could I sensibly add it so as to avoid this sort of defeater for R? That's the question and it's difficult to give a general principled answer to it. Ric Otte tries to do so. Tim O'Connor and I (separately) propose ways a naturalist might know R and so not get a defeater via Plantinga's argument. Plantinga has replies to all of us that are worth reading.

I do think it's tricky to know what you could add to N&E to avoid his problem. Of course I favor my response to Plantinga, which is in that anthology mentioned above. I'm less confident than I used to be that Plantinga's replies don't work. I guess my thought is that my sort of reply won't work in the XX ingestion case. So the question is why (and whether) it will work in the N&E case.


Brad Weslake said...

I think the problem is going to come in earlier, in the assignment of a low probability to P(R/N&E). Plantinga relies (in part) here on an argument that physicalism entails content epiphenomenalism. All such arguments are (I contend) unsound. For remarks along these lines see the review by John Post of the Beilby anthology.

Jacob Russell Wintersmith said...

Does video of the debate exist, by any chance?