Sunday, September 27, 2009

Inference to the Best Explanation (Abductive Inferential Reasoning, as explained by Alister McGrath)

Tonight I'm spending time reading Alister McGrath's new book A Fine-Tuned Universe: The Quest for God in Science and Theology. McGrath is an excellent writer and great scholar, with two doctoral degrees, one in molecular biophysics and the other in theology (both from Oxford). McGrath is also a Jesus-follower.

In F-TU McGrath begins by devoting several chapters to his method, which is arguing by inference to the best explanation, or what has also been called abductive inference. Traditional theological arguments use deductive inferential reasoning, such as William Lane Craig uses in the Kalam Argument for God's existence. (McGrath, 40) While such an argument can be compelling, it remains that there are difficulties with this approach, "not least that it is obliged to invoke at least one strong a priori causal principle as a premise (such as the "principle of sufficient reason"). For these and other reasons, many have drawn the conclusion that it is not possible to deduce the existence of God from general principles." (Ib.)

OK. Such arguments give us no logical certainty. But in my mind they do not intend to. Admittedly this is unclear since the use of a valid deductive argument form, such as the Kalam Argument uses, still depends on premises that are only inductively arrived at. So I think the Kalam Argument is an inductive argument for God's existence, albeit a very strong inductive argument.

McGrath then states that abductive inferential reasoning provides a way of reasoning that avoids the pitfalls of deductive-causal argumentation. He writes: "Yet an argument that proves unable to compel assent by demonstrating the existence of God as a necessary inference can nevertheless still be the best explanation of what is observed. Its public performance lies not in its deep logical structures, but in its capacity to bring in to harmony the often-conflicting in the human experience of reality. The explanatory capacity of the natural sciences and Christian theology rest in part on their ability to disern coherence or unity within what otherwise might seem epistemic turbulence and phenomenological chaos." (Ib., 40-41)

Very nice. Abductive, inference-to-the-best-explanation reasoning, avoids some of the epistemic pitfalls of deductive reasoning. Consider this from McGrath, whicd really sums up nicely what he is doing: "Whether we consider anthropic phenomena or theories of the origin of ethics, it proces impossible to make any form of deductive argument from what is observed to either naturalism or theism. Yes it remains perfectly fair to ask what the best explanation might be of these matters." (Ib., 41)

I am impressed and interested. I'm now thinking that one could make nice, fruitful comparisons between what McGrath here gives us and what N.T. Wright offers us by way of his discussions of competing "narratives."