1. Intervention and Causation
Intervention and Causation:
A Philosophical Perspective
Victor Gijsbers
(Philosophy, Universiteit Leiden)
2012-10-05

2. Causation
● A central topic in modern philosophy.
● Why believe that philosophy could teach us
something about causation?
● The idea and use of philosophical analysis.

3. Intervention
● Central notion in current debates: intervention.
– Pearl, Causality (2000)
– Woodward, Making Things Happen (2003)
● Using intervention to understand causation.
● Why is that a good idea?

4. Overview
● Causation seems to be:
– important,
– modal.
● Main development in theories of causation:
– From reductive analyses
– to interventionist analyses.

5. Importance of causation
● Why do scientists care about causation?
● “The law of causality, I believe, like much that
passes muster among philosophers, is a relic of
a bygone age, surviving, like the monarchy,
only because it is erroneously supposed to do
no harm.”
– (Russell, On the Notion of Cause, 1912)

6. Importance of causation
● Science is interested in functional relations.
– pV = NkT
– number of people infected = F(population
density, quality of sanitation, availability of
hospitals, …)
– P(number of people infected) = F(population
density, quality of sanitation, availability of
hospitals, …)
● So why be interested in causation?

7. Importance of causation
● The functional relations by themselves are not
guides to action.
● We want to know about cause and effect.
● But what is the relation between causation and
functional relations?

8. Causation and modality
● Some of our statements are about what actually
happens; others are about modal facts.
– What could happen.
– What must happen.
– What would happen, if...
● Modal statements play an important role in
planning, justifying, assigning blame and credit.

9. Causation and modality
● Causation seems to be closely linked to
modality.
● If A caused B, then, if A had not happened, B
would not have happened.
● That doesn't quite work... but intuitively,
something in the vicinity should.

10. Causation
● Summarising, causation seems to be:
– important
– modal.
● Suggestive links with action (but at this point,
no more than suggestive).

11. Reductive theories
● Reductive, regularity theories of causation.
– Modal facts have to be reduced to facts about
what actually happens.
– Actions should not appear in the theory.
● Why? Because our scientific knowledge is
based on what we see. Anything else would be
superstition, pseudoscience, empty
speculation.
● And we only see what is actual.

12. Reductive theories
● Science is based on what we see.
● Objection: it is also based on what we do.
● Do → see → science.
● Doing falls out of the equation when we think
about the justification of our theories.

13. Reductive theories
● We want to analyse causation in terms of
observed relations between event types.
● Most simple theory is the constant conjunction
theory (Hume, 1748):
– A causes B ↔ whenever A happens, B happens
immediately afterwards
● Can be changed to accommodate probabilistic
relationships.

14. Counterexamples
● There is constant conjunction without
causation. For instance:
– Common cause structures.
– “Accidental” conjunction.
● Both are important to recognise in actual
scientific research.

15. Counterexamples
● Reductive theories fail to capture the modal
aspect of causation.
● They fail less often when we add more causal
variables. Still – this doesn't look like the right
way. There always remains the possibility of
accident.
● Which we can accept in practice, but not when
we want to know the meaning of causation.

16. Interventionism
● Very rough example of an interventionist theory
of causation:
– A causes B ↔ by intervening on A, we can
change B.
● Why would talking about interventions help?

17. Using intervention
● We do use interventions to test causal claims.
Is A a cause of B? We intervene on A, and
check whether B is still probabilistically related
to A.
– Yes? Causation!
– No? No causation!
● Both conclusions can be wrong.

18. Interventionism
● Haven't we just added another causal variable?
● Reductive way of thinking: we perform
interventions so that we can determine a set of
functional relationships that we are interested
in.
● The doing is merely there to serve the seeing.
● The possibility of accident remains.

19. Interventionism
● Remember our statement of interventionism:
– A causes B ↔ by intervening on A, we can
change B.
● This is an inherently modal claim. We set A = 1,
and what happens is B = 1. But this only counts
as a changing of B, if it is that case that had we
set A = 0, then B would not have been 1.
● Something counts as a successful intervention
only if the effect was not accidental.

20. Interventionism
● But why would modality be connected with our
doing of things?
● Because when we do things, we make choices.
[Insert difficult questions about free will here.]
● It is when we think about our future plans,
about what we want to change, and so on, that
we start thinking modally; and that we start to
get interested in causation.

21. Interventionism
● Beings who could only see things, but could not
do things, would not be interested in causation.
● What is more: they could not have the concept
of causation. We can only understand
causation because of the modality of action.
● It is therefore no surprise that a philosophical
analysis of causation must use a term like
'intervention'.

22. Conclusion
● But it is also no surprise that theories about
causal modelling and causal inference can
make good use of the notion of intervention.
● Because claims about causation turn out to be
claims about the effects of actions.
● Reminder: this is a controversial story!