Saturday, May 31, 2014

Heterogeneity according to Cartwright

Nancy Cartwright is one of the best philosophers of science around, in many people's opinion. I find her work particularly interesting for the new ways she offers of thinking about old ideas like "laws of nature" and the ways things work in the natural world. Much of what she writes about the entities and processes of the natural world is equally perceptive when applied to the social world. Especially interesting is her 1999 book, The Dappled World: A Study of the Boundaries of Science.

In The Dappled World Cartwright focuses on an idea that I've highlighted many times here as well -- the idea of the fundamental heterogeneity of the world. Here are the opening words of the book:
This book supposes that, as appearances suggest, we live in a dappled world, a world rich in different things, with different natures, behaving in different ways. The laws that describe this world are a patchwork, not a pyramid. They do not take after the simple, elegant and abstract structure of a system of axioms and theorems. Rather they look like — and steadfastly stick to looking like — science as we know it: apportioned into disciplines, apparently arbitrarily grown up; governing different sets of properties at levels of abstraction; pockets of great precision; large parcels of qualitative maxims resisting precise formulation; erratic overlaps; here and there, once in a while, corners that line up, but mostly ragged edges; and always the cover of law just loosely attached to the jumbled world of material things. (1)
She is particularly interested in demolishing the quest for scientific unity — a single unifying theory that can be said to represent the whole of a field of natural or social phenomena. She firmly rejects the idealized notion that quantum mechanics deductively encompasses all areas of physics, or that rational choice theory encompasses all areas of the social sciences. Instead, she argues that the “patchwork” nature of the disciplines of the sciences — different definitions of domain, different ideas about methodology and proof — corresponds in a deep way to the patchwork nature of the world. So methodology and ontology are intermingled.
The problem is that our beliefs about the structure of the world go hand-in-hand with the methodologies we adopt to study it. The worry is not so much that we will adopt wrong images with which to represent the world, but rather that we will choose wrong tools with which to change it. (12)
One way that Cartwright chooses to explain her “dappled” notion of the world is to insist that all scientific laws require ceteris paribus conditions. So scientific laws — even supposedly fundamental laws of mechanics like F = ma — do not apply unconditionally; rather, they apply subject to specific statements of boundary conditions and isolation conditions. A scientific experiment is designed in such a way as to exclude the workings of extraneous forces or influences; but Cartwright observes that in the real world of experience, we almost never observe this kind of isolation. Instead, baseballs are conveyed through parabolic arcs by mass, momentum, air currents, humidity, and fluid frictions — leading to a resultant arc which is only approximately described by the mathematical formula of the hyperbola (25-27).

The idea that the laws of nature always bring with them a set of ceteris paribus conditions is one way of pointing to the heterogeneous nature of the world. But a different way of characterizing the overall behavior of the spherical solid baseball is to refer to its nature — the inherent properties of the thing that work to produce its causal powers. The fact that it is a material object gives it a disposition to move in accordance with the laws of inertia and gravitation. The fact that it has a leather skin gives it a disposition to interact with surrounding fluids in ways that create patterns of micro-turbulence. The fact that its center of gravity is not at the geometrical center of the sphere gives it a tendency to wobble in flight. Each of these properties of the thing give separable tendencies to motion when the object is disturbed (hit with a baseball bat).

If we use the language of a thing's “nature” then the laws of nature are doubly secondary: they are approximate; and they derive from something more fundamental, the ensemble of natures that inhere in the objects in question.

Here are the three core ideas that she puts forward (4):
  1. The impressive empirical successes of our best physics theories may argue for the truth of these theories but not for their universality...
  2. Laws' where they do apply, hold only ceteris paribus....
  3. Our most wide-ranging scientific knowledge is not knowledge of laws but knowledge of the natures of things...
One consequence of Cartwright's views here, and her skepticism about the universality and generality of scientific laws, is a principled rejection of reductionism:
Not only do I want to challenge the possibility of downwards reduction but also the possibility of 'cross-wise reduction'. Do the laws of physics that are true of systems ... in the highly contrived environments of a laboratory or inside the housing of a modern technological device, do these laws carry across to systems, even systems of very much the same kind, in different and less regulated settings? (25)
And her answer to these questions is negative.

Cartwright's position has a lot in common with current work on causal powers, and this extends to her appeal to Aristotelian metaphysics as an alternative to Humean theories of regularities.
What kinds of facts (if any) determine the behaviour of a nomological machine? The Humean tradition, which finds nothing in nature except what regularly happens, insists that it must be further regularities. This chapter will continue the argument that laws in the sense of claims about what regularly happens are not our most basic kind of scientific knowledge. More basic is knowledge about capacities, in particular about what capacities are associated with what features. (77)
Where do laws of nature come from? ... It is capacities that are basic, and laws of nature obtain ... on account of the capacities; or more explicitly, on account of the repeated operation of a system of components with stable capacities in particularly fortunate circumstances. (49)
The idea of a nomological machine plays a central role in Cartwright's arguments; so what does this amount to? Cartwright is clear and explicit about this question:
What is a nomological machine? It is a fixed (enough) arrangement of components, or factors, with stable (enough) capacities that in the right sort of stable (enough) environment will, with repeated operation, give rise to the kind of regular behavior that we represent in our scientific laws. (50)
So a nomological machine is an important way of linking capacities and laws in Cartwright's account: it is a bundled set of special circumstances that give rise to the sorts of strong regularities that Humeans are looking for. But Cartwright's key point is that these circumstances are very special indeed: controlled laboratory setups and isolated technical devices are the examples she offers. This gives substance to the three core ideas articulated above: crucially, the construct illustrates the lack of universality and generality for scientific laws that she thinks is ineliminable in the study of nature (and society).

Cartwright develops these ideas largely in the context of the physical sciences. But she has been an important contributor to the philosophy of economics and the social sciences as well. And her skepticism about governing laws is even more compelling in the latter realms. As I tried to articulate the point in “On the Scope and Limits of Generalizations in the Social Sciences" (1993; link), we should think of regularities in the social world as phenomenal rather than governing. The social regularities we observe are the consequence of the workings of social mechanisms, and we should not imagine that there is an underlying set of governing laws that "generate" the social world.

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