Krister Segerberg on Logic of Actions PDF
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Outstanding Contributions to Logic 1 Robert Trypuz Editor Krister Segerberg on Logic of Actions Outstanding Contributions to Logic Volume 1 Editor-in-Chief Sven Ove Hansson, Royal Institute of Technology Editorial board Marcus Kracht, Universität Bielefeld Lawrence Moss, Indiana University Sonja Smets, Universiteit van Amsterdam Heinrich Wansing, Ruhr-Universität Bochum For furthervolumes: http://www.springer.com/series/10033 Robert Trypuz Editor Krister Segerberg on Logic of Actions 123 Editor RobertTrypuz The JohnPaulIICatholicUniversity ofLublin Lublin Poland ISSN 2211-2758 ISSN 2211-2766 (electronic) ISBN 978-94-007-7045-4 ISBN 978-94-007-7046-1 (eBook) DOI 10.1007/978-94-007-7046-1 SpringerDordrechtHeidelbergNewYorkLondon LibraryofCongressControlNumber:2013945289 (cid:2)SpringerScience+BusinessMediaDordrecht2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. 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While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. ThephotographyinthecovertakenbyStenLindström Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Part I Krister Segerberg’s Philosophy of Action. . . . . . . . . . . . . . . . . . . . . . 3 Richmond H. Thomason The Concept of a Routine in Segerberg’s Philosophy of Action. . . . . . 25 Dag Elgesem On the Reconciliation of Logics of Agency and Logics of Event Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Jan Broersen Three Traditions in the Logic of Action: Bringing Them Together . . . 61 Andreas Herzig, Tiago de Lima, Emiliano Lorini and Nicolas Troquard Deontic Logics Based on Boolean Algebra . . . . . . . . . . . . . . . . . . . . . 85 Pablo F. Castro and Piotr Kulicki Dynamic Deontic Logic, Segerberg-Style . . . . . . . . . . . . . . . . . . . . . . 119 John-Jules Ch. Meyer Part II Contraction, Revision, Expansion: Representing Belief Change Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Sven Ove Hansson Segerberg on the Paradoxes of Introspective Belief Change . . . . . . . . 153 Sebastian Enqvist and Erik J. Olsson v vi Contents Equivalent Beliefs in Dynamic Doxastic Logic . . . . . . . . . . . . . . . . . . 179 Robert Goldblatt On Revocable and Irrevocable Belief Revision . . . . . . . . . . . . . . . . . . 209 Hans van Ditmarsch Actions, Belief Update, and DDL. . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Jérôme Lang DDL as an ‘‘Internalization’’ of Dynamic Belief Revision . . . . . . . . . . 253 Alexandru Baltag, Virginie Fiutek and Sonja Smets Two Logical Faces of Belief Revision. . . . . . . . . . . . . . . . . . . . . . . . . 281 Johan van Benthem Appendix A: Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Appendix B: Some Metaphilosophical Remarks . . . . . . . . . . . . . . . . . 319 Appendix C: Bibliography of Krister Segerberg. . . . . . . . . . . . . . . . . 323 Introduction Theconceptsofactionandagencybelongtothecategoryofthoseconceptswhich arenoteasytodealwith.Avastamountofliterature onthe philosophyofaction, thelogicofactionandagencyandbroadlyunderstoodAIprovesthesewordstobe true.Thedifficultyoneencounterswhenanalysingtheconceptsinquestionliesin their complex nature manifestedby their strong relationship with mentalattitudes (such as beliefs, desires and intentions), practical reasoning (consisting of delib- eration, means-end reasoning and decision process), plans and routines, will, agent’s abilities, time (a well-known problem of temporal extension of actions), responsibility and causality binding mental attitudes with bodily motions and action’sresults.ThusstartingfromAristotle,throughAnselmofCanterburytothe newopeninginthephilosophyofactioninitiatedbyElizabethAnscombe,wecan countmanywaysofexplaininganddefiningwhatactionandagencyare(almostas many as there are philosophers who have been writing about them). It also has to be emphasised that many issues concerning the notions of action and agency studied previouslyinphilosophy,inparticularthosebeinginthescope ofinterest of philosophical logic, have recently found their creative continuation (in some cases got even their second life) in computer science, especially in AI, planning and knowledge representation. Situation Calculus, Dynamic Logic, a family of BDIlogicsortheinsightgivenbygametheory:Alternating-timeTemporalLogic andCoalitionLogicarejustafewexamplesofartefactscreatedtosolveproblems in computer science. Notwithstanding the fact that the aforementioned theories havebeendevelopedinthescopeofcomputerscience,itisobvioustodaythatthey point out problems relevant also to philosophy (frame problem being just one of many examples). While talking about actions, it is useful from the very beginning to distinguish between real actions and doxastic (or epistemic) actions. Real actions are actions having some manifestation in the environment external to the agent. We may metaphorically call such actions ‘‘tangible’’. Doxastic or epistemic actions are actions changing agents’ beliefs and knowledge about the environment as well as about other beliefs. We may also call the actions in question ‘‘intangible’’, since they do not have physical presence in the environment. Krister Segerberg is a philosopher who for more than 30 years has been ana- lysing intricacies of real and doxastic actions by means offormal tools—mostly modal (dynamic)logic anditssemantics.He hashadsuch asignificant impact on vii viii Introduction modallogicthat‘‘ItishardtoroamforlonginmodallogicwithoutfindingKrister Segerberg’s traces’’, as Johan van Benthem noted in [Van-Benthem-Ch, p. 18]. Krister Segerberg himself admits in [24]: ‘‘I am a supporter offormal methods in philosophy.ThisisnottosaythatIbelievethatallphilosophymustbemadewith theirhelp.[...]Myownviewisthatformalmethodsareimportantforsomeparts of philosophy and indispensable for a few.’’ KristerSegerbergwasalwaysopentoinsightsandproblemscomingbothfrom philosophy and computer science. Working on the border between the fields, he built many logical systems and conceptual frameworks, which resolved many issues in the theory of action and agency, contributing both to philosophy and computer science. A characteristic feature of his works is their outstanding philosophical depth connected with perfect logical skills. For the sake of presentation, the volume is divided into two parts. In the first part there are papers devoted to the real actions. In this part there are also papers takingintoaccounttheworksofKristerSegerbergondeonticlogicwhichhebuilt uponatheoryofrealactions.Thesecondpartofthevolumecontainsthepaperson the doxastic actions. Remaining part of this introduction briefly sketches the content of the two parts. It is also intended to be a sort of roadmap to Krister Segerberg’s works on actions and an incentive for many, in particular young, researcherstocontinuefurtherexploration.InfactitwasKristerSegerberg’swish toinvite youngresearcherstocontribute tothisvolume.Thusmanychapters, and thisintroductionaswell,havebeenwrittenbyyoungauthorsorareco-authoredby young researchers. Richmond Thomason’s chapter in the first part of the volume and Sven Ove Hansson’s chapter in the second part of it can be seen as a much more mature and experienced continuation of this introduction. Real Actions Variety ofapproaches towards actionscan bedivided intotwomain streams. The first stream prefers to refer to actions directly and to study them as events of certain kind. In the second stream actions are out of the picture—instead of referring to actions, one studies how the states of affairs (or events) are brought aboutbyagents,orhowtheagentsareresponsibleforthestatesofaffairs.Itshould bealsomentionedthatquiterecentlytherehavebeenattemptstocombinethetwo approaches together by creating formal languages enabling at the same time to refer to actions and express agent’s responsibility. Actions as events. In the first approach towards actions actions are events. ‘‘There is no action without a corresponding event’’—writes Krister Segerberg in [71, p. 303]. In most of the works on the philosophy of action, ‘‘action’’ is syn- onymouswith‘‘intentionalaction’’,meaninganactiondonewithintention[4,45] ordoneforareason[13,6],whichissupposedtodifferentiateitfromunintentional behaviour or reflex. Some philosophers researching actions, e.g., Donald David- son,claimedthatactionsareeventsandindeed‘‘nothingisaddedtotheeventitself Introduction ix that makes it into an action’’ [14]. What distinguishes events which are actions from those which are not, is the fact that the former are caused by some pro- attitudes.However,asDavidsonputs it,‘‘thisisan addition tothedescription we giveoftheevent,nottotheeventitself’’[14].Thereforeitisclearthatdespitethe fact that mental attitudes are necessary for the presence of an action, they are not ‘‘part’’ofit.TheotherpointofviewisrepresentedforinstancebyJohnSearle.In [46]hestatedthat‘‘thewholeactionconsistsoftwocomponents—theintention-in- action and the bodily movement’’. In case of a premeditated action, an action is additionally preceded by practical reasoning. Similar definition of action we find in [57, p. 161], where Krister Segerberg states ‘‘To understand action both are needed, agent and world, intention and change’’. The concept of change for Krister Segerberg, much like for George Henrik von Wright [99], is a transition between two states: prior and posterior ones. Theory of change, developed in von Wright’s theory offacts, was formally clarifiedandcomparedtoclassificationofverbs1byKristerSegerbergin[64,65]. According to Krister Segerberg, intention is directed towards change (an event) [54,57].Theintentionwhichtriggersanactionmustbeoperational,i.e.,thereisa routine[58]whichanagentcanrundirectlyinordertofulfilhisintention.‘‘Todo something is to run a routine. To be able to do something is to have a routine available. To deliberate is to search for a routine.’’ [58, p. 188]. The process of searching for a routine Krister Segerberg calls ‘‘deliberation walk’’, which is in practice aprocessofspecificationofthestartingintentioninordertofindtheone whichisoperational.Bydeliberationwalkanagentendsupwiththeintentionset consisting of the intentions linked or ordered in specific way, the last one being operational. In order to find out with which intention an action was carried out, Krister Segerberg introduces the infimum property which states that the last intention in the set is the one with which the agent’s action is carried out. In [50] he states that an action triggered on the basis of operational intention cannot usually guaranteeinwhich posterior stateanagent willend up.Krister Segerberg seestheroleofintentionasafunctionwhichrestrictsallpossibleoutcomesofthe action to those which are intended. That concept of intention as a function was a source of inspiration for the authors of chapter [Herzig-Ch]. Theideaofactionsaseventsfound itsformalrepresentationinmanyworksof Krister Segerberg.2 In [50, 51, 54, 55, 57] one can find non-dynamic logics of action.Thepapers[50,54,57]containaninterestingstudyoftheconceptofaction andintention,whereanactionisinterpretedasanintention-outcomepair.Moreon this subject one can find in chapter [Elgasem-Ch] of this volume, in Sect. 4, Segerberg’s formal characterisation of intentional actions. Another logic with actions, where action complement was interestingly ana- lysed (by referring to the interior operation in topology), has been introduced in 1 Cf.[96]. 2 Please see [63, 80, 88] for the outline of the logic of action and agency from Krister Segerberg’sperspective. x Introduction [55].In[34,p.1203]wefindastudyofsuchoperatorsas:‘‘aisabouttodoe’’,‘‘a has just finished doing e’’, ‘‘because of a’s action, e is just about to be realized’’ and ‘‘because of a’s action, e has just been realized’’. OtherformalsystemsofKristerSegerbergrefertopropositionaldynamiclogic (PDL) created by Vaughan R. Pratt for describing and analysing computer pro- grams (cf. [42, 43]). PDL was brought to the philosophical ground by Krister Segerberg. In 1980 he wrote about PDL: ‘‘This paper is perhaps the first one to present it to a philosophical audience’’ [49, p. 276]. Richmond Thomason describes Krister Segerberg’s approach in chapter [Thomason-Ch, p.2] in the following words: KristerSegerberg’sapproachtoactiondiffersfromcontemporaryworkinthephilosophy of action in seeking to begin with logical foundations. And it differs from much con- temporaryworkinphilosophicallogicbydrawingondynamiclogicasasourceofideas. Thecomputationalturnmakesalotofsense,foratleasttworeasons.First,aswenoted, traditional philosophical logic doesn’t seem to provide tools that are well adapted to modelling action. Theoretical computer science represents a relatively recent branch of logic,inspiredbyanewapplicationarea,andwecanlooktoitforinnovationsthatmaybe of philosophical value. Second, computer programs are instructions, and so are directed towardsaction;ratherthanbeingtrueorfalse,acomputerprogramisexecuted.Alogical theoryofprogramscouldwellservetoprovideconceptualrigouraswellasnewinsights tothephilosophyofaction. Krister Segerberg also provided an intuitive and extensive way of under- standingprogramesasactionsbyreferringtotheconceptofroutine[58].Wehave already quoted his motto, ‘‘To do something is to run a routine. To be able to do somethingistohavearoutineavailable.Todeliberateistosearchforaroutine’’ [58, p. 188]. Extensive and critical study of the Krister Segerberg’s concept of routineispresentedinchapter[Elgasem-Ch]ofthisvolumebyDagElgasem.The chapterintroducescentralelementsofKristerSegerberg’saccountofroutinesand relatesittootherpositionsinthephilosophyofaction.Itisarguedthattheconcept of a routine has an important role to play in the theory of action and that Krister Segerberg’s own formalisation of the concept of intentional action does not meet the theoretical challenges posed by the routine concept. It is pointed out that to meetthechallengesitisenoughtobringtheconceptofaroutineexplicitlyintothe semantic framework of the logic of intentions and actions. Krister Segerberg introduced manyinteresting dynamic operators and provided adequate(i.e.,soundandcomplete)axiomatisationforPDL(cf.[47,53]3andmany otherinterestingformalresultsin[48,52]).Languageofdynamiclogicwithoper- ators‘‘after’’and‘‘during’’isdefinedinBackus-Naurnotationasfollows[49,52]: u::¼p j:uju^uj½a(cid:2)uj½½a(cid:2)(cid:2)u ð1Þ i a::¼a ja(cid:3) jataja;a ð2Þ i 3 DecidabilityofPDLwasprovedin[18].ThehistoryofearlyresultsinPDLcanbefoundin [20].
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