Saturday, November 07, 2009

Inference To the Best Explanation

A new logic text that has just come my way is The Power of Critical Thinking: Effective Reasoning About Ordinary and Extraordinary Claims, by Lewis Vaughn (Oxford). I have reviewed this text and think it is excellent and creative. It's colorful, contains many excellent and relevant explanations, and is clearly written. And, it contains a chapter on "Inference To the Best Explanation." This is the first logic text I have seen that explains this. For these reasons I am considering changing to this text for my logic classes next fall.

Inference to the best explanation (IBE), also called abductive reasoning, is important for Christian theologians to understand. For example, Alister McGrath's new work on the fine-tuning argument for God's existence in his A Fine-Tuned Universe: The Quest for God in Science and Theology depends on it. An understanding of inference as to the best explanation is helpful in adjudicating between competing metanarratives. (On abductive reasoning as IBE, see Atocha Aliseda, Abductive reasoning: logical investigations into discovery and explanation, pp. 134 ff.)

What, exactly, is IBE? Vaughn writes: "In inference to the best explanation, we reason from premises about a state of affairs to an explanation of that state of affairs. The premises are statements about observations or other evidence to be explained. The explanation is a claim about why the state of affairs is the way it is. The key question that this type of inference tries to answer is, What is the best explanation for the existence or nature of this state of affairs? The best explanation is the one most likely to be true, even though there is no guarantee of its truth as there is in deductive inference." (344)

Inference as to the best explanation has this pattern:

1. Phenomenon Q.
2. E provides the best explanation for Q.
3. Therefore, it is probable that E is true.

In my Philosophy of Religion courses I use Pojman's text. It contains Robin Collins's fine-tuning argument for the existence of God, which uses IBE. Collins calls IBE "the prime principle of confirmation." This is: whenever we are considering two competing hypotheses, an observation counts as evidence in favor of the hypothesis under which the observation has the highest probability (or is the least improbable). For example, suppose I walk out in the hall after class and a hundred pennies are on the ground, spelling “John, call home now.”
The prime principle of confirmation (IBE) tells me that this did not happen by chance. Some causal agent probably did this. Therefore it is probable that this happened by design. The fine-tuning evidences are like this, only much more so.

Vaughn writes: "Notice that an inference to the best explanation always goes "beyond the evidence" - it tries to explain facts but does so by positing a theory that is not derived entirely from those facts. It tries to understand the known by putting forth - through inference and imagination - a theoretical pattern that encompasses both the known and the unknown. It proposes a plausible pattern that expands our understanding. The fact that there are best explanations, of course, implies that not all explanations for a state of affairs are created equal." (344-345)

Vaughn gives us 45 pages in clear explanation of inference to the best explanation. Thank you!