REVIEW 4 major objections 5 minor 42 references
Searching for actual causes: Approximate algorithms with adjustable precision
T0 review · 4 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read This paper claims that Halpern-Pearl actual causes can be identified by a beam search over counterfactual interventions, using a user-supplied oracle, in polynomial time with adjustable precision.
desk verdict A useful, honest engineering contribution to approximate HP actual causes; the formal precision claim is weaker than advertised, but the empirical scope is new and the code is real. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the space of interventions $E$: each element is a set of variable-value pairs, split into the counterfactual pairs $e_C$ and the actual-value contingency pairs $e_W$. An HP cause $C$ with contingency set $W$ is exactly the counterfactual part of some intervention $e$ that cancels the target predicate ($\phi(e)=0$) and is minimal under inclusion. The search itself is a beam search: at each depth it keeps only the $b$ most promising partial interventions according to a heuristic $\psi$, uses the oracle $\phi$ to decide whether the target still holds, and discards candidates that are supersets of causes already found. The ISI variant exploits the causal graph by replacing variables in a found cause with their parents and searching smaller sub-instances, and the LUCB variant replaces the deterministic oracle with confidence-bounded sampling when evaluations are stochastic.
What would settle it
Take a small Boolean SCM whose HP-cause set is known by exhaustive enumeration, run the base algorithm with an exact oracle and a beam wide enough to keep every candidate at every depth, and compare the output; if the output differs from the enumeration, the claimed intervention-space encoding or the minimality filter is wrong.
Extended reading notes
Core claim
The paper's central claim is that every HP cause of a target fact can be represented as an intervention $e$ in the space of variable-value assignments, where the variables set to counterfactual values form the cause $e_C$ and the variables kept at their actual values form the contingency set $e_W$. Finding the HP causes therefore reduces to finding interventions for which the target no longer holds ($\phi(e)=0$) and whose counterfactual part is minimal under inclusion. The base algorithm performs a beam search guided by a heuristic, evaluates candidates through the oracle $\phi$, and prunes any candidate that is a superset of an already found cause; the ISI algorithm repeats this search on sub-instances built from the causal graph; and the LUCB algorithm estimates $\phi(e)$ by confidence-bounded sampling when the system is stochastic. The authors claim this yields a polynomial-time approximation of the full HP-cause set, with complexity $O(|V|^2 \times |D_{\max}| \times b \times N_C \times |C_{\max}|)$, and that the beam size $b$ is an adjustable precision-exhaustiveness-runtime tradeoff.
Load-bearing premise
Correctness depends entirely on the user-supplied answer function: it must truthfully report whether the target outcome would still happen under every conceivable intervention, including counterfactual worlds that may be unrealistic or unobservable.
Editorial extensions
If this is right
- Actual-cause identification no longer requires explicit structural equations: any system that can answer counterfactual queries, such as a simulator or a hand-built expert model, can be searched directly.
- Non-Boolean discrete domains are handled natively, so causes can be reported as variable-value facts rather than only as boolean on/off events.
- For stochastic systems, repeated sampling and confidence bounds turn the search into approximate identification with user-set tolerances and sample budgets.
- The beam-size parameter is a practical control: larger beams increase precision and exhaustiveness at roughly linear runtime cost.
- When the causal graph is known, the ISI algorithm generally improves both accuracy and runtime by decomposing the search into smaller sub-instances.
Reading between the lines
- If the oracle is a learned counterfactual model, its errors propagate directly into the reported causes; a natural next experiment is measuring how oracle noise degrades precision and recall.
- The intervention-space encoding connects minimal HP causes to $L_0$-distance counterfactual explanations, suggesting the same beam search could serve as an explanation engine for black-box classifiers.
- The confidence-bounds machinery in LUCB points toward a formal anytime guarantee: as the sample budget grows, the estimated $\bar\phi(e)$ converges to $\phi^*(e)$, so a PAC-style statement of the search's precision is a testable extension.
- Because the reference sets for the non-Boolean and black-box experiments are assembled from the algorithms' own outputs, an independent exact enumeration for those settings would be a natural follow-up.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes three algorithms for identifying Halpern-Pearl (HP) actual causes in structural causal models: a beam-search base algorithm that explores interventions with an oracle for the target predicate, an iterative sub-instance identification (ISI) variant that uses the causal graph, and a LUCB-based stochastic evaluation method. The authors claim polynomial complexity and an adjustable precision-exhaustiveness tradeoff, and present experiments on Boolean, non-Boolean, black-box, and stochastic versions of the 'Steal Master Key' scenario. The paper is clearly written and includes code, but the central approximation guarantee is not established, and the evaluation for the non-Boolean and black-box cases relies on reference sets built from the algorithms' own outputs.
Significance. If the claims held, the work would fill a real gap: practical identification of HP actual causes in non-Boolean, black-box, and stochastic systems, beyond the Boolean logic-formula setting of ILP-based approaches. Strengths include the explicit oracle-based formulation, the concrete algorithmic descriptions, the availability of code, and the use of an exact exhaustive reference set for the base and noisy SCMs. The empirical comparison with ILP is useful. However, the central notion of 'adjustable precision' is not backed by any formal bound relating beam size to precision or recall, and the experiments for non-Boolean and black-box systems use circular reference sets. The polynomial complexity claim is output-sensitive and not a worst-case guarantee. These gaps are load-bearing for the paper's main contributions, but they are fixable within the manuscript's scope by either adding guarantees, weakening the claims, or providing independent ground truth for small instances.
major comments (4)
- [4.3.1-4.3.2, Algorithm 1] The central claim that Algorithm 1 identifies HP causes with adjustable precision is not supported. In Section 4.3.2, filterMinimality only discards an element if a subset of its cause set has already been identified as a cause. Because beam search prunes nodes at each depth, a true HP cause can be pruned before being evaluated, and a superset of it can later be generated from another branch, evaluate to φ(e)=0, and be reported as a cause. This yields both false positives (AC3 violations) and false negatives even with a perfect oracle. No theorem or bound is given that relates precision or recall to the beam size b, the heuristic ψ, or the search depth. The experiments in Annex H quantify 'Overshoot' (non-minimal causes) and show it does not clearly decrease with beam size, confirming that the issue is real. Without such a bound, the phrase 'adjustable precision' is not justified.
- [5.6.2] The reference sets for the non-Boolean and black-box SCMs are constructed by running the algorithms themselves: the text states that for these models the reference set combines all identified causes across beam sizes and then filters non-minimal ones, and that precision and recall are 'an upper bound instead of being exact.' Annex H further notes that a recall value of 1 in the non-Boolean SCM is an artifact of this computation method. This circularity means the experimental results cannot support the abstract's claim that the algorithms identify causes for non-Boolean and black-box systems. The exact reference set used for the base and noisy SCMs (via unlimited beam) is a genuine benchmark and should be emphasized, but the broader claim needs either an independent ground truth for small instances or a clear statement that the non-Boolean and black-box results are illustrative only.
- [4.3.4 and Annex C] The claimed polynomial complexity is output-sensitive and not a worst-case guarantee. The stated bound O(|V|^2 × |D_max| × b × N_C × |C_max|) depends on N_C, the number of identified causes, which can be exponential in |V|. Section 4.3.4 acknowledges that 'N_C depends on the parameter of interest in an unclear way' but still concludes expect polynomial complexity. Annex C's empirical regressions are specific to the SMK scenario and show several regimes with low R² values (e.g., 0.099, 0.121, 0.283 in Fig. C.2), so they do not substantiate a general polynomial bound. The complexity claim should be restated as output-sensitive, or a bound on N_C should be provided under stated assumptions.
- [4.5 and Annex F] The LUCB algorithm is presented as a way to 'control the reliability' of stochastic cause identification, but no correctness or high-probability guarantee is proved. The stop conditions (1)-(3) are expressed in terms of sample averages and confidence bounds, yet there is no theorem showing that when the conditions are met, the true Bernoulli parameters satisfy the corresponding inequalities with the stated tolerance and confidence. The user-specified maximum number of samples in Algorithm 4 can terminate the procedure before the conditions are met, and the experimental results in Section 6.4 show LUCB sometimes performing worse than naive sampling. Without an analysis, the stochastic extension does not provide a formal reliability guarantee.
minor comments (5)
- [2.3] The name 'Halpren and Hitchcock' should be 'Halpern and Hitchcock'.
- [5.4] Equation (4) defines a distribution for X but does not explain the temporal dependence: the text says the value is flipped 'each time it is set,' which suggests a process over time, but the equation is given as a static conditional distribution. Please clarify the relationship between the flipping process and the equation.
- [Annex F, Algorithm 4] The functions updateUB and updateLB are referenced in Algorithms 5-7 but never defined; the confidence-bound formulas should be given explicitly so the reader can see how the bounds are computed and how they depend on the step t.
- [6.1] The label 'Base SMC' should read 'Base SCM'.
- [Figure H.7] The heuristic name 'okham' should be 'Occam' for consistency with the text.
Circularity Check
Core search algorithms are not circular, but the non-Boolean and black-box evaluation reference sets are built from the algorithms' own outputs, so the reported F1 scores for those systems are partly self-defined.
-
self definitional
[Section 5.6.2 and Annex H.1]
"To produce a reference set of causes, we created a set of all identified causes for a given context, combining the sets from every beam size used, from the base and ISI algorithms (when both were used). We then filtered out the non-minimal causes from this combined set. ... The recall score in the non-boolean SCM reaching 1 is an artefact of the computation method. Since our reference set of causes is built from the identified causes, when we find no cause at all, we have no reference."
The reference set used to measure precision and recall is not independently derived from the HP definition; it is defined as the union of causes identified by the algorithms themselves at various beam sizes. For the non-Boolean SCM, no independent minimality check (beam size -1) was performed, and for the black-box SCM the reference set is likewise generated from algorithm outputs. Therefore the reported F1, precision, and recall are partly measuring the algorithms against their own outputs; the 'expected causes' are by construction causes the algorithms already found. The paper explicitly acknowledges the recall value of 1 in the non-Boolean case is an artefact of this construction.
full rationale
The central identification algorithms are not circular in the sense of deriving their target from their inputs: Algorithm 1 is a beam search over interventions, evaluated by an oracle and filtered by minimality checks on the causes already found; Algorithms 2 and 3 build on this search using causal-graph structure and bandit confidence bounds, respectively. These constructions are independent of the HP definition's conclusion: the oracle supplies AC2 evidence, the algorithm checks minimality approximately, and the result is not built into the inputs. The beam-size pruning gap identified by the skeptical analysis is a correctness or approximation-guarantee issue, not a circularity: the absence of a bound relating beam size to false positives/negatives means the 'adjustable precision' claim is empirically supported but not proven, which is a validity concern but not a definitional reduction. There are self-citations (e.g., [34], [35], [36], [17]) but they are contextual (related work, relevance, and roadmap) and not load-bearing for the derivation; the formal load-bearing results are cited from external sources (Halpern, Lowerre, Kaufmann and Kalyanakrishnan). The one concrete circularity is in the evaluation methodology for the non-Boolean and black-box SCMs: the reference set is constructed from the union of the algorithms' own identified causes, so the measured agreement is partly self-referential. This affects the empirical claims but not the formal algorithm design, hence the score is moderate rather than high.
Assumptions & free parameters
free parameters (5)
- beam size b =
varied from 1 to 50 (and 0 to 100 for smallest-cause task)
- cancellation threshold epsilon =
0.3
- noise level epsilon_n =
0.01
- LUCB tolerances tc, tnc, tb =
1%, 1%, 10%
- batch size =
10
assumptions (5)
- domain assumption The Halpern-Pearl definition (AC1-AC3) is the target notion of actual cause.
- domain assumption Oracle phi correctly evaluates the target predicate under any intervention.
- domain assumption Every endogenous variable has a discrete and finite domain.
- ad hoc to paper The heuristic function psi is informative enough that top-b nodes contain the relevant causes.
- domain assumption For ISI, a superset of the true causal-parent relation is known.
Cite this review
Pith. "Pith review of Searching for actual causes: Approximate algorithms with adjustable precision." pith.science (2026). https://pith.science/paper/BOTP6ZBQ
@misc{pith2026250707857,
author = {Pith},
title = {Pith review of: Searching for actual causes: Approximate algorithms with adjustable precision},
year = {2026},
howpublished = {\url{https://pith.science/paper/BOTP6ZBQ}},
note = {Machine review of arXiv:2507.07857}
}
read the original abstract
Causality has gained popularity in recent years. It has helped improve the performance, reliability, and interpretability of machine learning models. However, recent literature on explainable artificial intelligence (XAI) has faced criticism. The classical XAI and causality literature focuses on understanding which factors contribute to which consequences. While such knowledge is valuable for researchers and engineers, it is not what non-expert users expect as explanations. Instead, these users often await facts that cause the target consequences, i.e., actual causes. Formalizing this notion is still an open problem. Additionally, identifying actual causes is reportedly an NP-complete problem, and there are too few practical solutions to approximate formal definitions. We propose a set of algorithms to identify actual causes with a polynomial complexity and an adjustable level of precision and exhaustiveness. Our experiments indicate that the algorithms (1) identify causes for different categories of systems that are not handled by existing approaches (i.e., non-boolean, black-box, and stochastic systems), (2) can be adjusted to gain more precision and exhaustiveness with more computation time.
Figures
Reference graph
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candidate causes
We first sample one batch of each element in the beam. We then update the confidences until they are all under the corresponding tolerance threshold, or we reach the maximum number of samples set by the user. When we update the confidence for the beam (see Algorithm 5), we fir...
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In IEEE International Conference on Au- tonomic Computing and Self-Organizing Sys- tems (ACSOS) (accepted)
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