Mechanisms, propensities, causation

Isabelle Drouet

Université Catholique de Louvain

Two approaches to mechanisms (Glennan 2002)

higher levelslevel of physics

thing, with stable dispositions

sequence of singular events

MDC, GlennanSalmon, Dowe

complex-system approachprocess approach

c-s mechanisms and difference-making

• several papers dealing with the relationship between c-s mechanisms and causality as counterfactual dependence (Woodward 2002, Psillos 2004, Glennan 2009)

• question: is it mechanisms or counterfactuals that are fundamental?

p mechanisms and counterfactuals

• Counterfactuals involved in the definitions of mark transmission and of causal interaction in Salmon 1984

• Reference dropped in Dowe and Salmon 1994: conserved quantity theory

Questions

• Can't we say something more concerning the relationship between p mechanisms and– counterfactuals – more generally, difference-making?

• Remark: p mechanisms / c-s mechanisms vs. possible / impossible to explain “genuinely singular events” (Glennan 2002)

Approach

• Focus on propensities

• Justification: – provide the only physical interpretation for

probabilities of singular events– have to do with p mechanisms

• NB. One goal of the talk is to explicate this justification.

Outline

1. Propensities and p mechanisms

2. Propensities and difference-making

3. p mechanisms and difference-making

Outline

1. Propensities and p mechanisms

2. Propensities and difference-making

3. p mechanisms and difference-making

Popper’s propensity theory

• An objective, physical interpretation of singular probabilities

• Propensities as tendencies of physical situations to produce singular events

• Physical reality of propensities• Probabilities as measures of propensities

Propensities and processes

• Ontological similarities: physically real, dynamic / active, causally productive, somehow continuous

• Yet no identity of (some) processes with propensities: processes ≠ tendencies

Salmon (1984) on propensities and processes

• Propensities = probas that are carried by indeterministic causal processes (203)

• Problems:- difficult to express in terms of conserved

quantities- misses the Popperian probability / propensity

distinction

Dowe (1992) on propensities and processes

• “propensities should be regarded as referring to the operation of indeterministic causal processes and interactions” (213)

• Relies only on (Popperian) propensities being attached to the level of physics

• Implies there are no propensities (although there may be objective, physical probas) but at the level of physics

Outline

1. Propensities and p mechanisms

2. Propensities and difference-making

3. p mechanisms and difference-making

Probabilistic causality

• Analyses of causality in terms of inequalities between absolute and conditional probabilities

• At the level of physics, problem with the interpretation of conditional probabilities

Humphreys' paradox (1985)

• (CI):if p(A / B) is temporally inverse and p is given

a propensity interpretation,then p(A / B) = p(A / non-B) = p(A)

• logically incompatible with the calculus of probability

• conclusion: no propensity interpretation of conditional probabilities.

Against HP

• Justification of (CI): if p(A / B) is inverse, impossible for the propensity tending to realize A to be (physically) modified by the occurrence of B

• But: according to the propensity theory, the production relation is between a physical situation and sg events, not between two sg events (conditioning and conditioned).

Towards a propensity interpretation of p(A / B)

• Conditionalization as a modification of p• A propensity interpretation tells how a new

probability function, meaning a new physical situation, is defined out the initial one and B

• The definition can be such that the properties of conditionalization are accounted for

• Csq: one can define probabilistic notions of singular causality at the level of physics

Link with counterfactuals

• The new situation has to be different from the initial, actual one, i.e. p(A / B)- measures the propensity of a counterfactual

situation to produce A- measures a counterfactual propensity to produce

A- is a counterfactual probability

• At the level of physics, notions of probabilistic causality collapse into counterfactual analyses.

Outline

1. Propensities and p mechanisms

2. Propensities and difference-making

3. p mechanisms and difference-making

What I have claimed

• propensities pertain to the level of physics and they refer to indeterministic causal processes and interactions

• probabilistic causality can be defined at this level and in terms of propensities, and there it collapses with the counterfactual approach

p mechanisms and difference-making

• p mechanisms are more fundamental than difference-making:• they give reference to the propensity talk• propensities are needed to ground a

difference-making notion of singular physical causality

• Conceptual and ontological priority

Scope

• Not a conclusion specific to p mech.• A conclusion

– about mechanisms and difference-making at the same level

– concerning mechanisms• What is specific to p mechanisms:

– irrelevance of the debate concerning counterfactuals and characterizations of mechanisms

– problem with the interpretation of conditional probabilities.