First Discussion on Deductive-Nomological Explanation

I would like to begin the class with unfinished business concerning Newton, Descartes, and Duhem. In particular, I would like to return to Newton's claim, "And so the true cause of the length of the image was detected to be no other than that light consists of rays differently refrangible, which . . . were according to their degrees of refrangibility, transmitted toward diverse parts of the wall." With reference to that claim, I'd like to re-examine the basis for Duhem's thesis that physical theories are not explanatory.

After discussing these matter, I would like to lecture a bit concerning features of the deductive-nomological model of explanation. In particular I hope to

• briefly remind you of the details concerning the conditions of the model.
• discuss the dependence of the D-N model on the notion of a law and sketch some of the difficulties concerning the distinction between laws and accidental generalizations.
• discuss the connections between the D-N model and Hume's view of causation.

After I've finished lecturing on these points (with plenty of interruptions for discussion), I'd like discussion to focus on

1. The intuition driving Hempel's model
2. How Hempel argues for the D-N model
3. How one should respond to the facts that explanations are typically not stated as arguments and that when reformulated as arguments, they typically fail to satisfy the conditions of the D-N model.

Although we may want to say a bit about the so-called "symmetry condition" (see pp. 249, 366f), we can defer that discussion -- along with the discussion of other objections raised by Scriven -- until next week, when we will be reading Scriven. Although we should note the problem of explanatory asymmetries (discussed on pp. 352-54), we should postpone careful consideration of the questions until April 24.

In connection with questions 1 and 2, I'd urge you to look carefully at pp. 246, 256, 337, 368.

In connection with question 3, I'd urge you to look at Hempel's discussion of Scriven's ink-spill example (pp. 360f), and of "self-evidencing" explanations (pp. 372-74).

Although I am not planning on raising any specific questions or points concerning section 12 of Popper's Logic of Scientific Discovery, feel free to raise any concerns that you may have.