Chemistry Reference
In-Depth Information
causally entail their targets. In so doing, idealized causal models can serve a
cognitive function by raising awareness of those factors that are not relevant to
our understanding of a phenomenon
s occurrence.
In spite of the considerable virtues of Strevens
'
account of scientific explanation,
this chapter makes the case that it fails to adequately capture the nature and function
of explanatory idealization in chemistry. Explanatory idealization in chemistry is
often a matter of distorting explanatorily relevant causal factors - the difference-
makers themselves. Strevens
'
commitment to an ontological conception of causal
explanation rules out the idealization of difference-makers because they undermine
the causal entailment of the target phenomenon. And in an ontological mode of
explanation, it is difficult to see how idealized models in chemistry could perform a
legitimate causal-explanatory function. For example, the ontological status of
atomic and molecular orbitals is vexed to say the least and therefore appear to be
poor candidates for causal-difference-makers in Strevens
'
sense.
This chapter argues that some of the most important developments in the
quantum chemical modelling of reaction mechanisms may well distort the
causal story but they cite
non
-causal factors that make a difference to their
explanatory targets. The development of molecular orbital approaches to the
studyofanimportantclassoforganicreactions - pericyclic reactions - provide
selection rules based on the
symmetry
of the molecular orbital wave functions
contributing most to a given chemical reaction in their class. Symmetry, it is
argued, is a non-causal difference-maker. One can provide a positive explanatory
function for idealized models even if those models distort our understanding of
the
causal
production of the target phenomenon. Thus one can retain the
difference-making criterion of explanatory relevance so long as one is prepared
to accept that not all explanation is causal. Strevens himself suggests that one
might
detach difference-making from causal explanation but he does not pursue
this for obvious reasons.
'
13.2 Causal Difference-Making and Idealized Models
Strevens defends the idea that scientific explanation is a matter of constructing
models citing causal factors that make a difference to the causal production of an
event or regularity.
1
A casual factor must play an essential role in (say) an event
s
occurrence in order to count as a causal difference-maker. This means one cannot
remove the factor without invalidating the “causal entailment” of the target - the
logical derivation representing the actual target
'
s causal production (
2008
, p. 72).
This requires a “setup” specifying laws, events and background conditions and
'
1
I focus on Strevens
ideas concerning explanation in deterministic systems.
'
