Scientific Explanation

1. Scientific Explanation • Suppose we assume that explanation and prediction of phenomena are the goals/purposes of science • Suppose we also assume that any account of scientific explanation needs to incorporate logic and experience • Hempel’s “D-N model” of explanation • D: Deductive • N: Nomological (i.e., law-like) • Hempel’s model is formal and deductive

2. Scientific Explanation E: An event to be explained: The water in my car radiator froze last night. How to explain this? • (Relatively) pure water freezes at 32 degrees. • My car radiator contains relatively pure water and the temperature last night was below 32 degrees. ------------------------------------------------------------ Therefore, E: (the water in my car radiator froze)

3. Scientific Explanation E: An event to be explained: The water in my car radiator froze last night. If some phenomenon, E, can be subsumed under law-like generalizations and initial conditions (i.e., derived validly from them), then that phenomenon is explained. Hempel’s model L1, L2 … LN (Relatively pure water freezes…) C1, C2 … CN (My car radiator contains and the temp is) -------------------- E

4. Scientific Prediction E: An event predicted: The water in my car radiator will freeze last night. Hempel’s model • (Relatively) pure water freezesat 32 degrees (L) • My car radiator contains relatively free water and the temperature tonight will go below less than 32 degrees (C1 and C2). -------------------------------------------------------------------- So, the water is my car radiator will freeze tonight (E).

5. Laws and causation The laws that function in the D-N Model of explanation are universal statements: these are statements of the form “whenever and wherever conditions F occur, then so always and without exception will certain conditions of another kind, G, occur.” Strictly speaking, a statement will be considered a law only if there are reasons to think it is true. But at least some laws (Galileo’s and Kepler’s) would not qualify… as they are known to hold only approximately.

6. Laws and causation More recently some, like philosopher/physicist Nancy Cartwright, have argued that all the so-called laws of physics are “tweaked” so as to make them fit exceptions. Cartwright, How the Laws of Physics Lie.

7. Laws and causation The account of laws (they are statements of the form “whenever and wherever conditions F occur, then…”) needs more however to rule out “accidental generalization”: For example, the true and universal statement “All the rocks in this box contain iron”. Compare it to: “All relatively pure water will freeze at 32 degrees [provided the altitude isn’t too high, the water too deep, etc.]” What makes them different (if they are)?

8. Laws and causation One intuition: the statement about water freezing presumes “causation” – that low temperature causes water to freeze – but “being in this box” does not cause a rock to contain iron. The philosophical problem of causation (thanks, again, to Hume): all we can mean by “a causes b” is that “b always follows a” (constant conjunction) We experience nothing like a “cement” or “glue” between the occurrence of a and subsequently that of b.

9. Laws and causation What makes them different (if they are)? Another intuition: (genuine) universal statements yield counterfactual conditionals, while accidental generalizations do not: E.g., “If my car radiator contained relatively pure water (though it does not) and the temp went below 32 degrees, that water would freeze”. E.g., “If this rock were added to box (which it is not), it would contain iron”.

10. Laws and causation What makes them different (if they are)? Hempel: we should at least note that genuine law-like statements can support explanations, while accidental generalizations cannot. AG: All the rocks in this box contain iron. This rock is in this box. ------------------------------------------------ This rock contains iron.

11. Challenges to the D-N Model • This is not a universal account of explanation: • Some sciences include probabilistic generalizations from which only probable explanations and/or predictions follow. (Hempel does acknowledge this and offers a statistical covering law model.) • More importantly, some sciences – including biology – do not have any laws. Are they not able to offer explanations? • Historically this led some to question whether biology (or the social sciences) were “real sciences”

12. van Fraassen’s account • Explanation is not a formal relationship (defined in terms of logic) between a law-like statement and some phenomenon • Many scientists and philosophers now see “understanding’ rather than explanation and prediction as the primary goal of science • Explanation in science is a pragmatic relationship – context and practice dependent: • “Why” questions are asked, and regarded as answered, within specific scientific contexts • To understand them (and what will count as an answer) requires knowledge of the scientific context within which they are asked.

13. van Fraassen’s account • Example: Why sex? • Reminders: • Answers will greatly vary depending on context (religious vs. scientific, and within different scientific epochs) • For evolutionary biologists it is a question because • If the name of the game is passing on one’s genes (or “reproducing” oneself), sex cuts down by half the relevant inheritance • It is also expensive in other ways: mating rituals, fighting (usually among males) for females; concerns over “paternity”, etc.