Common sense of the hokum variety 
Via Brian Leiter and Mohan Matthen, I came across Alvin Plantinga's review in the New Republic of Thomas Nagel's newbook. Nagel and Plantinga both deny that life on Earth could have developed naturally, without any explicit purpose. For Nagel, who is an atheist, purpose is supposed to be something intrinsic to nature. For Plantinga, who is a theist, purpose is impressed on nature by God.

So both reject the naturalistic, Darwinian account of how life developed. Plantinga quotes Nagel as complaining that it's "a heroic triumph of ideological theory over common sense." Further down, he writes, "Nagel supports the commonsense view that the probability of this happening in the time available is extremely low, and he believes that nothing like sufficient evidence to overturn this verdict has been produced." Since this latter quote uses Plagtinga's own words, we get them both endorsing the idea that the naturalistic account violates the common sense view of the world.

As some commenters demonstrate, it's easy to ridicule this talk of common sense. One reason that common sense philosophy collapsed, after all, is that 19th-century know-nothings claimed that all of their dogmas were common sense.

Common sense as originally articulated by Thomas Reid is substantially more subtle.* For Reid, common sense is about faculties of belief formation rather than about specific propositional beliefs. Reliance on our senses is common sense, which means that seeing is prima facie grounds for believing. It is impossible to get enquiry started at all without provisional trust in the operations of our senses, memory, and reason. That trust in the first place is a trust in the faculties rather than in any specific beliefs formed by them.

Note that common sense, understood in Reid's way, doesn't include any specific beliefs. So it doesn't include any specific beliefs about origins of life and the universe.

Yet, I concede, common sense quickly yields some specific judgments. When I see a cat on the mat, I do employ my faculty of perception and judge 'A cat is on the mat'. Yet it is unclear what faculty is supposed to license 'The development of life would be inexplicable without there being some purpose'. I do not look and see it, nor do I receive it from any of the faculties which I trust at the outset of enquiry.

So Nagel and Plantinga are just appealing to common sense in that horrible, know-nothing sense that sunk common sense philosophy.

Plantinga goes on to explicate Nagel's argument by what seems to me to be an equivocation between probability, conditional probability, and likelihood. Further on, though, he parts company with Nagel. Where Nagel wants there to be purposes in nature itself, Plantinga wants them to be put in by God.**

Plantinga's idea is that the existence of God makes life and universe rather more probable than anything else would. He writes, "Given theism, there is no surprise at all that there should be creatures like us who are capable of atomic physics, relativity theory, quantum mechanics, and the like." In a sense, this is simply false. Everyone in the early 20th-century, whether theist or not, found relativity and quantum mechanics to be surprising.

He can reply here by saying that the capability is unsurprising, even if the content itself was a surprise. Theism explains why we can know things, because it posits that God made us to be knowers. Yet, accepting that God gave us truth-apt cognitive faculties, He still gave us limited capacities. Although we can figure out quantum mechanics, there are more complicated things we can't figure out. Why should he not have made our limits different, so that quantum mechanics would be forever beyond our ken?

If we take that question seriously, then it might be surprising even for theism that we are capable of quantum mechanics. If we scoff at the question, then we should not pretend to assign objective prior probabilities to there being creatures just like us given that a god exists. Those probabilities could not be anything more than our own subjective bleatings.

As I've argued elsewhere, arbitrary priors are the opposite of what Reid would have considered common sense.* So, to sound the drum again, the common sense of Nagel and Plantinga is the know-nothing hokum variety.


* For more discussion of this point, see my paper on Reid.

** Regarding the explanation of life in the universe, Plantinga comments that "God himself is living." The theology-cum-biology perplexes me, because I don't see how this could possibly be true in any scientifically useful sense of living.

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