Faculty
Research Interests
Selected Publications
Reviews
Grants, Fellowships and Honors
Work in Progress: Books
Teaching
Horacio Arló Costa received his Ph.D. from Columbia University. He is a department member since 1998. He is the director of the Major in Logic and Computation and an Associate of the Center for Philosophy of Science of the University of Pittsburgh. He has been an editor of the Journal of Philosophical Logic since 2004. He is also part of the funding editorial staff of the Review of Symbolic Logic and an area editor (epistemology) of Synthese..
Research Interests
My research has focused on work in different branches of philosophical logic, formal epistemology, decision theory and behavioral decision theory. Recent research on philosophical logic and formal epistemology has centered on: (1) probabilistic models for conditionals and nonmonotonic notions of consequence, (2) epistemic logic, (3) first order modal logic and (4) belief revision. A detailed presentation of these items and the papers related to them appears in the following section.
In 2005 Jeff Helzner (Columbia University) and I initiated a research program whose main target is the analysis (empirical and theoretical) of decision situations under indeterminacy of the sort that appear in the Ellsberg scenario. Part of his research agenda is focused on testing experimentally the psychological theories that intend to explain nonBayesian behavior via the postulation of psychological effects; and in comparing the explanatory power of some of the normative theories that intend to rationalize nonBayesian behavior. More recent work considers the case of decisions from experience and description. It is well known that these two types of decisions lead to dramatically different choice behavior in the case of risk. We have recently studied the case of uncertainty, verifying that the two types of decisions lead to rather different choice behavior as well in the case of uncertainty.
Herb Simon’s seminal ideas about bounded rationality has recently been extended and enriched by the work of Gerd Gigerenzer and collaborators. Paul Pedersen (CMU) and I have recently studied some of these heuristics, like Take the Best (TTB) and the Priority Heuristics. In the first case we studied the choice function that characterizes the heuristic extending it beyond binary choice. In the case of the priority heuristics we proposed an extension of the heuristics to the case of uncertainty. The mathematical model of TTB is part of a general program to present an empirically grounded theory of choice in general domains.
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Some Publications
Recent work in Formal Epistemology and Philosophical Logic.
(I) Bayesian Epistemology.
The work related to (1) is part of a larger foundational program studying the scope and limits of probabilistic strategies in Bayesian epistemology. The idea of these foundational strategies is to propose a notion of probability as the sole epistemological primitive and derive all other epistemological notions (belief, conditional belief, belief change) from this sole probabilistic primitive while avoiding some of the wellknown paradoxes in this area (like the paradox of the lottery). Unified probabilism achieves this goal by positing a notion of supposition (conditional probability) as the unique epistemological primitive. Bas van Fraassen proposed the central ideas of unified probabilism in an article in 1995. In a series of papers from 1999 to 2005 I proposed slight modifications and extensions of the theory and more recently I considered applications in the area of conditional logic (in collaboration with Rohit Parikh). The theory has nevertheless important limitations. The notion of iterated change derivable from it makes sense for a notion of `matter of fact supposition’, while it seems inappropriate as a general notion of belief change.

Valuebased Contraction: A Representation Result (with Hailin Liu)

Conditional Probability and Defeasible Inference (with Rohit Parikh), Journal of Philosophical Logic 34, 97119, 2005.
 Bayesian Epistemology and Epistemic Conditionals: On the Status of the ExportImport Laws, Journal of Philosophy, Vol. XCVIII, 11, 555598, 2001.
 Iterative probability kinematics, Journal of Philosophical Logic, 00, 46, 2001 (with Richmond Thomason)
 Hypothetical Revision and Matteroffact Supposition, 8th. International Workshop on MonMonotonic Reasoning, special session on Belief Change, Computer Research Repository, Los Alamos, ePrint Archive, ACM and NCSTRL. An extended version is published in Journal of Applied NonClassical Logics, special issue on Belief Change: Theory and Practice, Vol. 11, No 12, 2001.
DS
 “Twoplace probabilities, beliefs and belief revision,” Proceedings of the Twelfth Amsterdam Colloquium, Paul Dekker (ed.), 16, 1999 (with Rohit Parikh)
 “Qualitative and Probabilistic Models of Full Belief,” Logic Colloquium'98, Lecture Notes on Logic 13, S. Buss, P.Hajek, P. Pudlak (eds.), ASL, A. K. Peters, 2543, 1999.
(II) Belief Revision.
My work on belief revision explores the logical and conceptual consequences of thinking of a rational change in view as a cognitive decision. The decision theoretic account of contraction that thus arises has formal properties that are deviant with respect to some of the classical notions of contraction available in the literature like AGM. In collaboration with Isaac Levi I recently provided a complete axiomatization for this type of contraction. I also studied the case when cognitive decisions are done under conditions of value indeterminacy. Finally I considered the structure of a theory of belief change where the underlying notion of rationality is bounded (in the sense articulated by H. Simon and G. Gigerenzer). Part of this work is intimately connected with recent work in the theory of choice functions in social choice. Conceptually these issues address broader topics studied in formal epistemology.
 Social Norms, Rational Choice and Belief Change, forthcoming in Science in Flux, E. Olson (ed.) (with A.P. Pedersen).
 Indeterminacy and Belief Change, forthcoming in Logic, Epistemology and the Unity of Science, S. Rahman and J. Symons (eds.), Springer.
 Belief revision and Formal Epistemology, forthcoming in the Blackwell
Companion to LatinoAmerican Philosophy, O. Bueno (ed.).
 Rationality and Value: The Epistemological Role of Indeterminate and AgentDependent Values, forthcoming in: 8 Bridges Between Mainstream and Formal Epistemology, special issue of Philosophical Studies, (ed.) Vincent F. Hendricks.
 Contraction: On the decisiontheoretical origins of minimal change and entrenchment, forthcoming in Synthese (with Isaac Levi).
 DecisionTheoretic Contraction and Sequential Change, forthcoming in E. Olsson (ed.), Knowledge and Inquiry: Essays on the Pragmatism of Isaac Levi, Cambridge University Press, Cambridge.
 Decision Theoretic Contraction and Value Indeterminacy: Maximizing rather than Optimizing, Proceedings of the Sixth Workshop on Nonmonotonic Reasoning, Action, and Change, NRAC'05, (eds.) Leora Morgenstern and Maurice Pagnucco, 2005.
 Iterated abduction and Conditional Coherence, Proceedings of the Ninth Conference on Theoretical Aspects of Rationality and Knowledge, TARK IX, (ed.) Moshe Tennenholtz, 2003.
(III) Epistemic and modal logic
Work in areas (2) and (3) has focused on the study of the family of first order classical modal logics. This family of logics includes the first order normal modal logics as well as an interesting class of nonnormal modal logics, like nonadjunctive logics used to model qualitative probability as well as nonmonotonic logics of the type used by Nozick to model knowledge as truth tracking.
In a recent article in collaboration with Eric Pacuit, we proved a general completeness result for the entire class of first order classical modal logics in terms of general neighborhood frames with constant domains. The result shows that if one uses suitable extensions of semantical techniques first proposed by Scott it is possible to interpret the most comprehensive class of modal logics (normal and nonnormal) in terms of models and frames with constant domains. This includes some notorious normal systems like FOL+K, which in the Kripkean tradition is usually studied in terms of frames with varying domains.
 First Order Classical Modal Logic, Studia Logica, 84, 2, 171210, 2006
(with Eric Pacuit).
 Tracking truth: Knowledge and conditionals in the context of branching , Formal Epistemology Workshop, (eds.) B. Fitelson and S. Sarkar, 2006
(with R. Parikh)
 NonAdjunctive Inference and Classical Modalities, Journal of Philosophical Logic, vol. 34, no56, 581–605, 2005.
 First order extensions of classical systems of modal logic: The role of the Barcan schemas, Studia Logica, 71, 2002, 87118.
(IV) Conditional Logic
My work in this area is mainly related to probabilistic models of conditionals (see section (I)) and epistemic models of conditionals.
 Two notions of epistemic validity, Synthese, volume 109, No.2, 217262, November 1996 (with I. Levi)
 Rational Choice and Conditional Obligation, manuscript CMU, 2009 (with A.P. Pedersen)
 On a counterexample to the Ramsey Test proposed by Van McGee, manuscript CMU, 2009.
 The Logic of Conditionals, entry for the Entry for the Stanford Encyclopedia of Philosophy, 2007.
 Belief revision conditionals: basic iterated systems, in Annals of Pure and Applied Logic 96, 328, 1999.
 Epistemic conditionals, snakes and stars, in Conditionals, from Philosophy to Computer Science, vol. 5 of Studies in Logic and Computation [Series editor: D.M. Gabbay], L. Farinas del Cerro, G. Crocco, A. Herzig (eds.), Oxford University Press, 193239, 1995.
 Two notions of epistemic validity, Synthese, volume 109, No.2, 217262, November 1996 (with I. Levi).
 Maps between conditional logic and nonmonotonic logic, in Principles of Knowledge Representation and Reasoning: Proceedings of the Third International Conference, B. Nebel,C. Rich, W. Swartout, (eds.), San Mateo, CA.: Morgan Kaufmann, ), 553565, 1992 (with Scott Shapiro).
 Conditionals and monotonic belief revisions: the success postulate, Studia Logica XLIX,4, 557566, 1990.
(V) Philosophical Logic and natural language interpretation
These papers reflect an interest in the developing of a notion of dynamic semantics for natural language.
 Epistemological foundations for the representation of discourse context, forthcoming in Studies on Language and Information (CSLI), Stanford.
 Epistemic context, defeasible inference and conversational implicature, Proc.Context '99 P.Bouquet et al.(eds.), Lecture Notes in Artificial Intelligence, 1688,Springer, Berlin, 4253, 1999.
 A Theory of Contextual Propositions for Indicatives, CONTEXT 2003, Lecture Notes in Artificial Intelligence 2860, Fausto Giunchiglia, Patrick Blackburn, Chiara Ghidini, and Roy Turner (eds.), SpringerVerlag, BerlinHeidelberg, 15 28, 2003.

Contextual Modals, Proceedings of The Fifth International and Interdisciplinary Conference on Modeling and Using Context, (eds.) Anind Dey, Boicho Kokinov, David B Leake and Roy M. Turner, Springer Verlag, Lecture Notes in Artificial Intelligence, 2005 (with William Tysom).
(VI) Rational choice, normative and behavioral decision theory
 Knowing and supposing in games with perfect information, Studia Logica, 86, 3, 2007, 353373. Special issue on formal epistemology, edited by B. Fitelson, (with C. Bicchieri).
 Bounded Rationality: Models of some fast and frugal heuristics, forthcoming in Games, Norms and Reasons: Logic at the Crossroads, A. Gupta and J. van Benthem (eds.), Springer (with A.P. Pedersen).
 Iterated Random Selection as Intermediate Between Risk and Uncertainty, Proceedings of the Sixth International Symposium on Imprecise Probabilities and their applications, ISIPTA'09, 2009 (with Jeff Helzner).
 An extension to uncertainty of the Priority Heuristics, manuscript CMU, 2009 (with A.P. Pedersen)
 Ambiguity Aversion: the explanatory power of indeterminate probabilities, forthcoming in Synthese (with Jeff Helzner, special issue on the foundation of the decision sciences)
 Choice, Context and Ambiguity: Introduction, forthcoming in Synthese (with Jeff Helzner).
 Knowing and supposing in games with perfect information, Studia Logica, 86, 3, 2007, 353373. Special issue on formal epistemology, edited by B. Fitelson, (with C. Bicchieri).
 On the Explanatory Power of Indeterminate Probabilities, Proceedings of the Fifth International Symposium on Imprecise Probability: Theories and Applications, G. de Cooman, J. Vejnaroá, M. Zaffalon (eds.), 2007, 117125 (with Jeff Helzner).
 Risk, indeterminacy and decision, Proceedings of the ESSLI 2006 Workshop on Rationality and Knowledge, R. Parikh and S.Artemov, eds., 2006 (with Jeff Helzner).
 Comparative Ignorance and the Ellsberg Phenomenon, Proceedings of the Fourth International Symposium on Imprecise Probabilities and their applications, ISIPTA’05, 2005 (with Jeff Helzner).
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Reviews
 Review of Degrees of Belief, Franz Huber and Christoph SchmidtPetri (eds.) Synthese Library 342, Springer, 2009, forthcoming in Notre Dame Philosophical Reviews.
 Review of Frederic Schick’s Ambiguity and Logic, forthcoming in Studia Logica.
 Review of Paul Humphreys's Extending Ourselves: Computational Science, Empiricism, and Scientific Method, Oxford University Press, 2004, forthcoming in Mind.
 Review of Sherrilyn Roush’s, Tracking Truth: Knowledge, Evidence and Science, Oxford University Press, 2006, Notre Dame Philosophical Reviews, 2006.
 Review of David Christensen's Putting Logic In Its Place: Formal Constraints on Rational Belief, Oxford University Press, 2005, Journal of Philosophy, 2006.
 Essay Review of David Papineau's The Roots of Reason: Philosophical Essays on Rationality, Evolution, and Probability, Cambridge University Press, 2002, published in Notre Dame Philosophical Reviews, http://ndpr.icaap.org/, December 2003
 Review of Sven Ove Hansson’s The Structure of Values and Norms, Cambridge Studies in Probability, Induction and Decision Theory, 2001, History and Philosophy of Logic, 2005.
 Critical Notice of Defeasible deontic logic, D. Nute (ed.), Kluwer Academic Publishers, 1997, in Studia Logica, Volume 60, Issue 2, March 1998.
 Epistemic logic and the theory of games and decisions, M.O.L. Bacharach, L.A. GerardVaret, P. Mongin and H.S. Shin (eds.), Theory and Decision Library, Kluwer Academic Publishers, 1997, in Studia Logica, 1998.
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Work in Progress: Books
 Formal Epistemology: Fundamental Papers, (with Vincent Hendricks and Johan van Benthem), under contract in Cambridge University Press, forthcoming 2010. The book contains fundamental papers in various branches of formal epistemology (decision theory, probability, belief revision, epistemic logic, etc). Each section is introduced by essays written by the editors.
 Three essays in Formal Epistemology: Normative and Bounded Models of Rationality. In preparation.
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Grants, Fellowships and Scientific Collaborations
 Collaboration with the Cognitive Neuroscience Section of NINDS/NIH (Jordan Grafman) and SDS/CMU (Robyn Dawes and Coty Gonzalez). The main focus of the collaboration consists in a series of experiments with patients with prefrontal lesions. Most of the patients have frontotemporal dementia so VBM analysis is performed in order to correlate cognitive deficiencies with significant grey matter loss in areas of the vmPFC. fMRI studies with normal patients are performed at the NINDS/NIH facilities in Bethesda and analysis of data, behavioral experiments with normal subjects and software production is done by the CMU counterpart. The collaboration started in 2006. VBM analysis is currently being performed at NIH.
 Collaboration with Jeff Helzner (Columbia University) for a series of experiments on ambiguity aversion and related topics in behavioral decision theory. The collaboration started in 2005 and is currently ongoing.
 NEH Award. From 06/01/2004 thru 08/31/2004. Topic: C.I. Lewis notion of
coherence and its interest for contemporary epistemology.
 Visiting Professor, Department of Computer Science, CUNY, Graduate Center, during Spring and Summer 2004. This resulted in collaborations with Rohit Parikh and Eric Pacuit, that are now published (see above).
 Falk Humanities Research Grant (20012003). The grant was awarded in order to fund experimental work in models of decision making for a period of two years.
The project focuses on two issues. On the one hand it proposes a series of experiments concerning the role of emotions in decision making. A considerable amount of clinical and conceptual work has been recently devoted to reverse the traditional idea that emotions are sand in the machine of rational decision. Part of the evidence focuses on patients with prefrontal lesions. These patients lack the capacity of attaching valence to options. Several experiments correlate prefrontal lesions with an alleged incapacity for decision making and planning. Nevertheless these results seem based on limited models of decision making and on partial (and sometimes theoretically biased) data. More sophisticated models of decision are proposed and tested both with prefrontal patients and normal subjects.
The second aspect of the project is designed to test some procedural models of decision making in well know problematic scenarios (Ellsberg's paradoxical situations, preference reversals). Normative models appealing to indeterminate probabilities and values are also tested, considering their capacity to accommodate recalcitrant data (usually considered symptomatic of irrational behavior). Some experiments are designed to test the impact of valence on the adoption of heuristics in choice behavior.
 Appointed as an Associate of the Center for Philosophy of Science of the University of Pittsburgh (2000).
 Falk Humanities Research Grant (Summer 1998).
 Participate in a section (on Structures of Knowledge and Structures of Reasoning) of a National Project of MURST (Ministry of University and Scientific Research/Italy) on Knowledge and Cognition. The project provides money for travel, the organization of symposia, and expenses related to the edition of a book on computational and philosophical models of context.
 Game theoretic models for multiagent interactions, National Science Foundation NSF, Information, Robotics and Intelligent Systems, other PI's are C. Bicchieri, R. Parikh. 19992002. The project focuses on one of the main challenges of “utilitarian” Distributed Artificial Intelligence (DAI), i.e. how to apply noncooperative gametheoretical tools in order to model interactions of artificial agents. Various papers written in collaboration with the main PI's are now published (examples are: “Conditional probability and defeasible inference,” August 2001, (with Rohit Parikh); “Knowing and supposing in games with perfect information”, June 1999/January 2000 (with Cristina Bicchieri)).
 Whiting Doctoral Dissertation Fellowship (19956).
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Teaching
Courses recently taught at Carnegie Mellon University include:
 Language and Thought (80181)
 Philosophy of Mind (80270)
 Logic in Artificial Intelligence (80314/614)
 Modal Logic (80315/615)
 Seminar on Philosophy and Methodology (80512)
 Seminar on Epistemology (80518/818)
 Minds Machines and Knowledge (80600)
 Rational Choice (80305)
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