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Actual causality for everything in life�thanks to Joe Halpern�

Hana Chockler

Department of Informatics

King’s College, London

IBM Research

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Actual Causality

A theoretical concept from AI

Extends causal counterfactual reasoning

Enables us to reason causally

about a specific situation

that occurred in the past

©Halpern & Pearl, 2001

+

…

@Joe Halpern – many definitions and results

Then Joe spent a sabbatical at the Hebrew University –

a key moment in my academic journey (I was a PhD student)

Hana Chockler, Joseph Y. Halpern:�Responsibility and Blame: A Structural-Model Approach. IJCAI 2003

Hana Chockler, Joseph Y. Halpern, Orna Kupferman:

What causes a system to satisfy a specification? ACM TOCL 2008

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Hana Chockler, Joseph Y. Halpern:�Responsibility and Blame: A Structural-Model Approach.

IJCAI 2003 and JAIR 2004

Quantification of causality,

allowing to rank causes by importance

To this day my most cited paper (I just checked again)

… also Joe’s 16^th most cited paper (which is not saying much)

Allows to focus on the most influential causes – very important for large practical applications

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Hana Chockler, Joseph Y. Halpern, Orna Kupferman:

What causes a system to satisfy a specification? ACM TOCL 2008

Took a very long time to get published…

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Formal Verification

A huge and difficult

to understand system M:

A correctness specification φ

Does M satisfy φ?

no

counterexample

yes

the system is correct!

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Does M satisfy φ?

no

counterexample

yes

the system is correct!

Do we understand the counterexample?

A correctness specification φ

A huge and difficult

to understand system M:

Do we really believe it?

Formal Verification

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Does M satisfy φ?

no

counterexample

yes

Do we understand the counterexample?

A correctness specification φ

A huge and difficult

to understand system M:

Do we really believe it?

Everything is actual causality!

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A huge and difficult

to understand system M:

A correctness specification φ

Does M satisfy φ?

no

counterexample

yes

the system is correct!

Hana Chockler, Joseph Y. Halpern, Orna Kupferman:

What causes a system to satisfy a specification? ACM TOCL 2008

Everything is actual causality!

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A huge and difficult

to understand system M:

A correctness specification φ

Does M satisfy φ?

no

counterexample

yes

the system is correct!

Ilan Beer, Shoham Ben-David, Hana Chockler, Avigail Orni, Richard J. Trefler:

Explaining Counterexamples Using Causality. CAV 2009 (and FMSD)

My second most cited paper

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Explaining counterexamples using causality�(Red Dots)�part of IBM tool

A timing diagram of a buggy hardware execution

φ = always ((!START and !STATUS_VALID and END) ->

next(!START Until (STATUS_VALID and READY))

causes marked as red dots

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Black-box reasoning about AI models’ decisions

Intervene on inputs

inputs

outputs

Input transformation

Observe the outputs

Reason about the way AI makes its decisions

One-node causal model

Hana Chockler, Joseph Y. Halpern:�Explaining Image Classifiers. KR 2024
Hana Chockler, David A. Kelly, Daniel Kroening, Youcheng Sun:�Causal Explanations for Image Classifiers. JAIR 2026

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Ongoing theoretical work with Joe: harm, fairness, neural networks

Hana Chockler, Joseph Y. Halpern:�On Testing for Discrimination Using Causal Models. AAAI 2022

Sander Beckers, Hana Chockler, Joseph Y. Halpern:�A Causal Analysis of Harm. NeurIPS 2022 and Minds and Machines 2024

Sander Beckers, Hana Chockler, Joseph Y. Halpern:�Quantifying Harm. IJCAI 2023,

… journal version under submission.

We last saw Joe on the 31^st of October 2025 in London and planned to start working on a new paper

A lot of ideas and future directions…

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Writing papers with Joe

Very ordered, meticulous about keeping all versions
Never just erased anything – always respectful to his co-authors
Some papers have %joe25 and up – that’s how many passes Joe made on the paper
Makes Latex impossible to read for anybody but Joe

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