Mechanisms and Laws: Clarifying the Debate - Mechanism and Causality in Biology and Economics - page 123

cannot (Sect. 3.1 ). We show further how the mechanistic perspective provides new
resources to ameliorate these extrapolation problems. In Sect. 4 we turn to the
epistemological issues. We reject Leuridan's claim that mechanistic models must
contain law statements, and we show how mechanistic knowledge contributes to the
search for stable generalizations. We conclude that continued debates over whether
mechanisms can replace generalizations are likely to be unproductive. We con-
clude, second, that by taking a mechanistic stance, one gains a new vantage point on
old problems about laws and a view to new problems about the construction,
evaluation, and revision of models of biological mechanisms.
2 Leuridan's Thesis
In his title, Leuridan asks, “Can mechanisms really replace laws of nature?” He
answers, “No.” In fact, Leuridan's positive thesis is much weaker than this title
suggests.
Before formulating this weaker claim, it is necessary first to clear up some
terminology. Leuridan defines laws as “generalization[s] describing a regularity,
not some metaphysical entity that produces or is responsible for that regularity”
( 2010 , fn 1). This definition ignores three traditional distinctions that have brought
much-needed clarity to the discussions of laws in the philosophy of science. First,
we distinguish laws (metaphysical entities that produce or are responsible for
regularities) and law statements (descriptions of laws). If one does not respect
this distinction, one runs the risk (as Leuridan does) of unintentionally suggesting
that sentences, equations, or models are responsible for the fact that certain stable
regularities hold. In like fashion, we distinguish regularities, which are statistical
patterns of dependence and independence among magnitudes, from generalizations,
which describe regularities. Finally, we distinguish regularities from laws, which
produce or otherwise explain the patterns of dependence and independence among
magnitudes (or so one might hold).
Let us now reconstruct Leuridan's real thesis. First, Leuridan endorses the
ground rule of our discussion. Strict law statements, as Leuridan understands
them, are nonvacuous, universally quantified, and exceptionless statements that
are unlimited in scope, apply in all times and places, and contain only purely
qualitative predicates ( 2010 , p. 318). Noting that few law statements in any science
live up to these standards, Leuridan argues that the focus on strict law statements
(and presumably also on strict laws) is unhelpful for understanding science. Instead,
he focuses on the concept of a pragmatic law (or p-law). Following Sandra Mitchell
( 1997 , 2000 , 2003 , 2009 ), Leuridan understands p-law statements as descriptions of
stable and strong regularities that can be used to predict, explain, and manipulate
phenomena. A regularity is stable in proportion to the range of conditions under
which it continues to hold and to the size of the space-time region in which it
holds ( 2010 , p. 325). A regularity is strong if it is deterministic or frequent. p-law
statements need not satisfy the criteria for strict law statements. Thus, Leuridan's