Mechanisms and Natural Kinds

Carl F. Craver

Washington University, St. Louis

Ccraver@artsci.wustl.edu

Mechanisms and Causality, Kent 9/09

To Sort the Phenomena: Elements

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To Sort the Phenomena: Minds

Memory

LTM

Non-Declarative (Implicit)

Declarative (Explicit)

Episodic (Events)

Semantic (Facts)

Priming Classical Conditioning

Motor Skills

Psychiatric Disorders

Boyd’s Homeostatic Property Clusters

• Natural kinds are clusters of properties that co-occur because of a homeostatic (similarity generating) mechanism.

• Normative Constraint: The correct taxonomy in a domain describes phenomenal kinds that correspond to the mechanisms constituting the causal structure of the world.

Questions and Theses

• HPC and Mechanisms: A heavenly match?• Can the mechanistic structure of the world serve as an

objective foundation for the taxonomy of natural kinds? • Can the idea of a “natural kind” survive if they are

understood in this way?• Main Theses:

– 1. The HPC view regresses.– 2. Pragmatic factors enter ineliminably into our consideration

of types of mechanisms.– 3. The concept of “natural kind” is unnecessary and

misleading in sciences such as neuroscience.

Outline

• 1. The HPC View and Its Motivations• 2. Taxonomic Revision: Lumping and Splitting• 3. Mechanisms• 4. Which mechanism?• 5. Kinds of Mechanisms• 6. Boundaries of Mechanisms• 7. Doing Without Natural Kinds

1. The Homeostatic Property Cluster Account of Natural Kinds

Conventionalism HPC Essentialism

Kornblith 1993; Wilson et al. forthcoming

Essentialists

• Natural kinds are defined by necessary and sufficient conditions.

Conventionalism HPC Essentialism

Common Objections to Essentialism

• Variability in Biological Populations

• Prototype Structure

Conventionalism

• There is no objective distinction between natural kinds and any other property cluster.

• Conventional kinds are “constructed along lines of family resemblance…. What puts things into a family is not nature, but people in concert.

• Promiscuity! (Boyd 1999)

Conventionalism HPC Essentialism

HPC Objections to Conventionalism

• Nothing in nature makes it the case that one member of the kind is relevantly similar to other members

• Prediction

• Explanation

• Control

• Indy Music?

HPC in SummaryNatural kinds are defined by:B1) Property Cluster: A cluster of properties that regularly

occur together.B2) Mechanism: A mechanism that explains why the

properties occur together. B3) Causal Import. The cluster figures in important causal

generalizations;B4) Maximal accommodation: Any refinement of the

definition of the kind either introduces causally and inductively irrelevant distinctions or glosses over causally and inductively relevant similarities.

B2) Mechanism: A mechanism that explains why the properties

occur together.• Prediction• Explanation• Control• To deny B2 yields a simple causal view: causally important

and maximally accommodated kinds.• But then, what does “natural kind” add over and above

“causally relevant variables.”• “The essential property that makes particular instances

members of the kind is their relation to that causal mechanism [that explains the cluster].

B3) Causal Import. The cluster figures in important causal

generalizations.• Pragmatic Reading: Useful.

– Slides toward conventionalism.

• Ontic Reading: Makes a difference to something.

• If deny B3: Simple metaphysical view of kinds: There are kinds wherever there a similarity generating mechanisms– Barometers, Storms, and Joint Pain.– Too weak for regimenting our taxonomies.

B4) Accommodation:• Weak Reading

– Members of the kind should be similar enough for our inferential uses of the kind and the instrumental projects that it facilitates (see Boyd 1999)

– Threatens the normative idea that the mechanistic structure of the world will arbitrate disputes over kindhood.

• Strong Reading– The correct description of a kind should be immune to revision in light of

further findings about the mechanistic structure of the world.– “consists in a certain accommodation between the relevant conceptual and

classificatory practices and independently existing causal structures” (Boyd 1997, 55).

– “The mechanisms that maintain any given HPC are part of the natural world, not simply our way of thinking about or intervening in the world” (Wilson 2005, 118).

– Should neither (i) gloss over causally relevant differences, nor (ii) recognize causally irrelevant differences.

2. Taxonomic Revision: Lumping and Splitting

Strategies for implementing the normative constraint that kinds

should track mechanisms.

The Splitting StrategyEmotion, Schizophrenia, Modularity, Memory

From McKusick (1969)

The Lumping StrategyFreud, Boyer, AIDS

From McKusick (1969)

Splitting, Lumping, and HPC

• When are two mechanisms of distinct kinds?

• When are two mechanisms of the same kind?

3. Mechanisms

• Entities• Activities• Organization

(Bechtel; Craver; Darden; Glennan; Machamer; Wimsatt; and so on)

4. Which Mechanism?

Which mechanism guides our taxonomic judgments?*membrane mechanism (b)*electrophysiological causes (a,d)*regulatory mechanisms*proximal antecedent causes*developmental causes*evolutionary causes

Keil also includes common effects.Reichenbach’s principle of common cause.Promiscuity!

Is this a problem?• Sometimes they coincide. Often not.

– Many etiological mechanisms, one constitutive mechanism.• HIV infection; clinical depression.

– One etiological mechanisms, different constitutive mechanisms• AIDS; Tertiary syphilis

– One and many etiological mechanisms at different stages• Needles, Sex, Transfusion -> HIV -> AIDS

• Psychiatric Cases– Different underlying mechanisms, same treatment groups

• Strong Accommodation (B4) – demands no further revision on the basis of the causal structure.

Two possibilities• Privilege one kind of mechanism

– Nothing in nature earns the privilege.

• Go pluralist.

– Weak Accommodation.

– What counts as “maximally refined” depends on your interests.

– Cannot settle disputes that arise from attention to different mechanistic entanglements.

Conventionalism HPC Essentialism

5. Kinds of Mechanisms• When Are Two Mechanisms Mechanisms of the

Same Kind?• HPC depends upon a notion of kinds of mechanisms

on pains of there being too many natural kinds.• Any detectable difference is a causal difference (has

import in the weak sense of B3).• Why not restrict to only those differences that alter

the property cluster? Because that presupposes that we know which properties belong in the cluster.

Regress

• Kinds of mechanisms?

• Kinds of entities, activities, and organizational features?

• Either way, we only stave off our ignorance of natural kinds a little longer.

The Scientific Problem

• HPC kinds tolerate variability.• HPC kinds tolerate multiple realization.• HPC kinds must be accommodated to the causal

structure of the world (B4).– If you characterize it too abstractly, you gloss over

causally relevant differences.– If you characterize it in maximal detail, every

mechanism is a kind unto itself.– What is the appropriate degree of abstraction?

A Textbook Hippocampus

A Computational Hippocampus

• A sequential Hopfield net?

• A feedback mechanism?

• A control mechanism

The Point

• Two mechanisms count as the same kind of mechanism according to one schema and as different kinds of mechanisms according to another.

• We have to balance generalization with the need to recognize causally significant differences.

• Such balancing is just of the sort of thing that depends on what we are trying to do.– Surgery?– Modeling?

A second response

• Go promiscuous! Accept all useful characterizations of the mechanism.– Glosses over causally relevant differences

(contra B4).– Reverses the direction of fit; accept the

mechanism schema when it is useful.

• What work is left for mechanisms to do?

To Summarize• HPC needs the notion of a kind of mechanism, and so

regresses.

• HPC needs to define an appropriate degree of abstraction in characterizing kinds of mechanisms.

• Appropriate degree of abstraction depends on what we intend to do with our description.

• What we intend to do with our description is a fact about how humans find it useful to cluster properties.

• The correct taxonomy of kinds depends on what we intend to do with it.

Conventionalism HPC Essentialism

5. The Boundaries of Mechanisms

• Which entities, activities, and organizational features are included in the kind of mechanism and which are not?

• The Ghost of Cartesian Mechanism

• What objective feature of the causal structure of the world binds entities, activities, and organizational features into a mechanism?

Where does one mechanism end and another begins

• Compartmentalization? (Protein synthesis)• Contact Action (Descartes)• Moving together• Stable across spatial translation (Ephemeral

mechanisms; cf. Glennan).• Strength of Interaction• Bandwidth of Interaction? (Better for cognitive

mechanisms than electrophysiology.• Relevance Boundaries!

Another way to make the point…• Glennan’s Law: All mechanisms are mechanisms

of or for something.• How one characterizes the phenomenon

determines (in part) what will count as an adequate mechanistic explanation for it.

• Kauffman’s articulation of parts.• Mechanisms are clustered into kinds because of

the property clusters they explain. • What objectivity is added by the appeal to

mechanisms over a cluster view?

Conventionalism HPC Essentialism

6. Pragmatics and The Ontic Conception

• Epistemic Conception: a phenomenon is explained by an argument showing that it was to be expected on the basis of the laws of nature.

• Ontic Conception (Causal): a phenomenon is explained by its causes and/or mechanisms.

• Salmon (1989)

Have I abandoned the ontic conception?

• NO!• 1) Mechanistic explanation is still grounded in the

causal structure of the world.• 2) Mechanistic explanations are fundamentally

particular; generalization into kinds is tinged by abstraction.

• 3) All explanations are relative to the choice of explanandum phenomenon (which is tinged with our interests) but from there, explanatory relevance is an objective matter.

• Though some ways of sorting mechanisms into kinds are more natural than others, there are no natural kinds of mechanisms (cf. Hacking, Rosey Dawn)

• We split when splitting makes a difference for our investigative or instrumental objectives.

• We lump when splitting makes no difference for our investigative or instrumental objectives.

• It is a fact, objective as any, whether a difference in mechanisms makes a difference for our investigative or instrumental objectives.

• Objective mechanisms are crucial for our taxonomies, but which taxonomy we find useful is always relative to our practical concerns.

6. Summary/Conclusion• Lumping and Splitting are common scientific strategies for

accommodating kinds to the mechanistic structure of the world.• The HPC account regresses.• The challenge of saying which mechanism matters for fixing

kinds.• The challenge of choosing the appropriate level of abstraction for

typing mechanisms.• The challenge of defining the boundaries of types of mechanisms.• This is only a problem if you think that there have to be natural

kinds but you want to accommodate the variability and multiple realizability of biological mechanisms.

• Give up the need for natural kinds in the special sciences.

Thanks to…

• Ken Aizawa, Matt Barker, Jim Bogen, Peter Carruthers, Lindley Darden, Carl Gillett, Todd Grantham, Ken Kendler, Max Kistler, Tom Polger, Georges Rey, Eric Seidel, Pamela Speh, Samuli Poyhonen, Dan Weiskopf, Rob Wilson, Petri Ylikoski.