American Law & Economics Association Annual Meetings

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1 Amercan Law & Economcs Assocaton Annual Meetngs Year 2004 Paper 21 Stablty and Change n Internatonal Customary Law Vncy Fon Francesco Pars The George Washngton Unversty George Mason Unversty Ths workng paper ste s hosted by The Berkeley Electronc Press (bepress) and may not be commercally reproduced wthout the publsher s permsson. Copyrght c 2004 by the authors.

2 STABILITY AND CHANGE IN INTERNATIONAL CUSTOMARY LAW Vncy Fon The George Washngton Unversty, Department of Economcs Francesco Pars George Mason Unversty, School of Law Aprl 2004 Abstract Whle customary law s capable of creatng unversally bndng rules, the rules that govern ts formaton allow states to gan an exempton from emergng norms of customary law by remanng persstent objectors. Ths form of objecton requres the objectng state to take express acton to oppose an emergng practce by makng ts objectons wdely known before the practce soldfes nto a bndng rule of custom. Lkewse, after the custom s formed states have an opportunty to express an objecton or depart from t. In ths latter case, the departng state does not obtan an exempton from the bndng custom unless other states acquesce to ts departure. We model the effects of persstent objector and subsequent objector doctrnes n the formaton and change of customary law when heterogeneous states are nvolved. We would lke to express our apprecaton to Dan Mlkove for hs nvaluable comments and suggestons. Hosted by The Berkeley Electronc Press

3 Vncy Fon 1 Francesco Pars 2 STABILITY AND CHANGE IN INTERNATIONAL CUSTOMARY LAW ABSTRACT: Whle customary law s capable of creatng unversally bndng rules, the rules that govern ts formaton allow states to gan an exempton from emergng norms of customary law by remanng persstent objectors. Ths form of objecton requres the objectng state to take express acton to oppose an emergng practce by makng ts objectons wdely known before the practce soldfes nto a bndng rule of custom. Lkewse, after the custom s formed states have an opportunty to express an objecton or depart from t. In ths latter case, the departng state does not obtan an exempton from the bndng custom unless other states acquesce to ts departure. We model the effects of persstent objector and subsequent objector doctrnes n the formaton and change of customary law when heterogeneous states are nvolved. JEL Codes: Keywords: K10, K33, D70 Customary law, Persstent Objector, Subsequent Objector, Norms. Custom consttutes a prmary source of nternatonal law, and has gven orgn to many rules that govern relatonshps between soveregn states. The bndng force of nternatonal customary law rests on the mpled consent of states. States express ther consent to be bound by a gven customary rule though ther own actons or practces. The process of custom formaton has struggled wth the vexng queston of how to promote stablty and relance on customary law, whle preservng the voluntary support of customary law n the flud envronment of nternatonal relatons. The balance between stablty and change n nternatonal customary law becomes partcularly complex n the face of dverse states preferences and changed crcumstances over tme. The rules that govern the formaton and applcaton of nternatonal customary law have themselves been the product of customary evoluton. The process of custom formaton s capable of creatng unversally bndng rules. At the same tme, ths process contemplates ways for unwllng states to gan exempton from emergng or exstng rules of customary law. 1 The George Washngton Unversty, Department of Economcs. We would lke to express our apprecaton to Dan Mlkove for hs nvaluable comments and suggestons. 2 George Mason Unversty, School of Law. 1

4 In ths paper we model the process of customary law formaton and consder two legal doctrnes that allow states to avod the bndng force of nternatonal customary law: the persstent objector and subsequent objector doctrnes. The frst doctrne gves objectng states an opportunty to avod, partally or entrely, the bndng force of an nternatonal norm by objectng to t. Under the subsequent objector doctrne, states can gan an exempton to depart from an exstng rule of customary law only by securng the acquescence of other states. Ths paper consders the effects of these two doctrnes when heterogeneous states are nvolved. The economc model reveals that the persstent and subsequent objector doctrnes mnmze the mpact of strategc objectons and departures from customary law, whle mantanng the flexblty necessary for adaptng custom to changed crcumstances over tme. By dong so, these nternatonal law doctrnes effectvely balance opposng needs for stablty and change n the evoluton of custom, whle preservng the voluntary bass of nternatonal customary law. Secton 1 provdes a stylzed explanaton of the rules that govern the formaton of nternatonal customary law and the role of the persstent objector doctrne n the formaton of custom. Secton 2 models custom formaton when states have an opportunty to opt out of emergng customs by nvokng the persstent objector doctrne. Secton 3 consders the role of the subsequent objector doctrne n custom formaton. Secton 4 extends the model to examne the workngs of the subsequent objector doctrne. Secton 5 compares the effects of the two doctrnes on custom formaton. 1. Internatonal Customary Law and Persstent Objector Doctrnes Relatvely few prncples govern the formaton of customary law. The theory of customary law defnes custom as a practce that emerges outsde of legal constrants and whch ndvduals, organzatons, and states follow n the course of ther nteractons, out of a sense of legal oblgaton. 2 Hosted by The Berkeley Electronc Press

5 1.1 Prncples on the Formaton of General Internatonal Customary Law When resoluton of a dspute requres applcaton of nternatonal customary law, an nternatonal trbunal verfes the presence of two formatve elements of a custom. These elements are generally referred to as the quanttatve element of practce, and the qualtatve element of opnon jurs. When both elements are present, the nternatonal practce gans the status of nternatonal customary law and states are consdered bound by the resultng custom. Wth respect to the frst formatve element, the emergence of an nternatonal customary law requres the presence of a stable and farly unform nternatonal practce wth whch many states have consstently compled. A tme lmt for complance s not defned; however, a long duraton helps to establsh that complance wth the practce was consstent, and also helps to clarfy the context and meanng of the practce. 3 Further, the practce should emerge from the spontaneous and uncoerced behavor of states. Restatements of nternatonal law refer to the consstency and generalty of the customary practce. The consstency requrement s not met f t s mpossble to dentfy a general practce because of fluctuatons n behavor. 4 More recent cases n nternatonal law restate the unformty requrement n terms of ncreasng and wdespread acceptance, allowng specal consderaton for emergng norms (or local clusters of multlateral practce) that are expected to become wdespread over tme. The second formatve element s generally dentfed by the phrase opno jurs ac necesstats, whch descrbes the requrement that the customary acton be perceved by states as fulfllng an essental norm of socal conduct. 5 Accordng to the opnon jurs requrement, states must act wth the belef that the appled practce s undertaken to fulfll an underlyng legal 3 Vller, 1985, p. 24. Stablty of the practce over tme s nterpreted wth some flexblty accordng to the crcumstances. There s no unversal mnmum duraton for the emergence of customary rules. Customary rules have evolved from both mmemoral practce and sngle acts. Stll, French scholars have tradtonally advocated the passage of forty years for the emergence of an nternatonal custom, whle German doctrne has generally requred thrty years. (Tunkn, 1961; and Mateesco, 1947). Naturally, the longer the tme requred to form a vald practce, the less lkely t s for custom to be an effectve substtute for treaty law (or formal legslaton, n the domestc settng), and to adapt to changng crcumstances over tme. 4 Regardng the nterpretaton of the condton of consstency or unversalty, nternatonal legal theory s ambvalent. Charney (1986) suggests that the system of nternatonal relatons s analogous to a world of ndvduals n the state of nature, and dsmsses the dea that unanmous consent by all partcpants s requred before bndng customary law s formed. 5 Ths element s also often descrbed as necessary and oblgatory conventon (Kelsen, 1939 and 1945; D Amato, 1971; Walden, 1977). 3

6 oblgaton, and that the practce s not followed by the state out of convenence or dplomatc courtesy durng a certan perod of tme. Ths requrement s amed at nsurng that customary law results from a general consensus of states, rather than from an occasonal and unqualfed convergence of state practce Persstent Objector Doctrnes and Specal Internatonal Customary Law In a multlateral settng, the formatve elements of a custom may be present only for a subset of states, or only for a lmted porton of the nternatonal practce. Internatonal law has developed legal doctrnes that govern the workngs of customary law when states have dfferent levels of partcpaton n a customary practce or when states have outrght opposed an emergng custom. Whle customary law s capable of creatng unversally bndng rules, for a fuller understandng of the process of nternatonal customary law formaton, t s mportant to consder the possblty that some states may attempt to gan exempton from emergng rules of general customary law by fully opposng a nascent custom or may trgger a specal blateral custom by partally opposng the nascent custom and complyng wth a lower behavoral standard. Some states have successfully argued that f they persstently object to an emergng rule of customary law, f and when a rule s formed t cannot be appled aganst them. These clams led to the gradual recognton of a prncple known as the persstent objector doctrne, allowng states to opt out of a new and otherwse unversal rule of nternatonal customary law by remanng persstent objectors (Brownle, 1990, p. 10; Kontou, 1994, p. 4; Sten, 1985, p. 457; and Wolfke, 1993, p. 66). 7 Objecton to an emergng custom may be full or partal. Full objecton sgnfes that the state does not accept and does not wsh to become bound by any part of the emergng custom. A partal objecton mples acceptance of some part of the custom. Partal objecton s generally found when states object by artculatng or mplementng a dfferent rule 6 Asylum and dplomatc mmunty rules are among the oldest examples of customs that emerged n lne wth these requrements. Already n ancent Greece the practces of grantng asylum for poltcal reasons and gvng mmunty to dplomatc mssonares were accompaned by the belef that those practces fulflled a fundamental necessty of nternatonal relatons, gven the fact that ther volaton would have serously undermned the stablty of peaceful relatons of states. See Kelley (1992) 7 For further dscusson of the persstent objector doctrnes n nternatonal customary law see also Akehurst ( ) and Charney (1985). For a dssentng vew on the legalty and desrablty of the persstent objector s exempton from customary law, see D Amato (forthcomng). 4 Hosted by The Berkeley Electronc Press

7 whch they consder preferable to the emergng custom. Full persstent objecton leads to a complete exempton from the emergng custom, whle partal objecton leads to a partal exempton from the rule. Once the custom soldfes, the porton of the custom that was not objected to bnds the partal persstent objector. Feasblty of the persstent objector doctrne was explctly supported by two well-known cases decded by the Internatonal Court of Justce. In Columba v. Peru, the Columban embassy granted poltcal asylum to a Peruvan natonal who was a leader of a mltary rebellon n Peru. The Peruvan government argued that the grant of asylum volated both a 1911 extradton treaty and a rule of customary law. The court ruled n favor of Peru, statng that Colomba faled to establsh exstence of a custom whch permts the state grantng dplomatc asylum to unlaterally defne an offense as poltcal. The court stated that snce Peru dd not ratfy the treaty n queston and specfcally repudated the asylum provsons, t would only be bound by nternatonal customary law. The customary rule governng asylum was however found not enforceable aganst Peru, because Peru persstently objected to such custom durng ts formatve stage. 8 Smlarly, n Unted Kngdom v. Norway, the court ruled that because the government of Norway had consstently opposed the terrtoral fshng zone regme, Norway was a persstent objector and therefore not bound by such customs. 9 To successfully nvoke the persstent objector doctrne two elements must be met. Frst, the objectng state must oppose an emergng customary practce by makng ts objectons wdely known before the practce soldfes nto a bndng rule of custom. Thus, the state must clearly object to the law from the moment of ts concepton or from the moment the state learns about any relevant practce or declaraton that may lead to the establshment of a custom. The objecton can be expressed n the form of statements, votes, or protests or can be mpled by abstanng from practce or adherng to a dfferent practce (Vller, 1985, p.15). 10 Second, the objecton to a practce must be consstent. Thus, the state must clearly object to the law from the begnnng and contnue to do so throughout ts formaton and beyond (Loschn, 1996, p. 150). A state may not 8 Asylum case (Columba v.peru), 1950 I.C.J. 266, Fsheres Case (Unted Kngdom v. Norway), 1951 I.C.J. 116, Accordng to Sten (1985, p. 458), n order for the doctrne to apply, t s suffcent that a state makes ts objecton manfest durng the process of the rule s emergence. See also the Fsheres Case (Unted Kngdom v. Norway), 1951 I.C.J. 116 (Judgment of December 18); Asylum Case (Columba v. Peru), 1950 I.C.J. 266 (Judgment of June 13). 5

8 adhere to a practce on some occasons and object to the practce on other occasons. A consstency requrement allows other states to rely on the poston of the objectng state and prevents the objectng state from beneftng from ambgutes n ts own course of acton. Two addtonal prncples govern applcablty of the persstent objector doctrne. The frst excludes applcaton of the persstent objector doctrne to nternatonal norms that are peremptory. A state may not nvoke the persstent objector doctrne f the customary law has acheved the status of jus cogens or mperatve law. 11 The second prncple provdes new states an opportunty to opt out of an exstng rule of nternatonal customary law. New states, and states that acheved ndependence after formaton of a custom, can obtan exempton from a prevously arsen custom f they object wthn a reasonable perod of tme Unformty and Dversty n Customary Law Tradtonally, nfluence of the persstent objector doctrne on formaton of nternatonal customary law was qute lmted (Sten, 1985). In the past the doctrne was rarely appled; states that dd not want to follow a rule smply attempted to refute ts exstence. Recent decades have seen a growng amount of offcal documentaton concernng the exstence and content of customary law (judgments of nternatonal courts, wrtng of publcsts, or declaratory treates). Wth ncreased awareness by the nternatonal communty and non-governmental organzatons of exstng nternatonal customs, states cannot easly confute an exstng customary rule and nvoke the persstent objector doctrnes to avod the bndng force of exstng custom. The greater accessblty and verfablty of general customary law has thus gven momentum to the persstent objector doctrne n the practce of nternatonal law (Loschn, 1996, pp ). The persstent objector doctrne offers a dssentng state a way to avod beng bound by specfc emergng customs, whle reaffrmng the legtmacy of the underlyng customary law process at the same tme. 11 Jus cogens encompasses peremptory rules that serve the most fundamental nterests of the nternatonal communty and that should be obeyed by all states wthout excepton (Loschn, 1996, pp ). Jus cogens prncples cannot be overrden by the persstent objector doctrne because jus cogens stands for fundamental and essental norms of justce whch no state can be allowed to dsobey (McClane, 1989, p. 25). 12 The reason that newly ndependent states are gven tme to gan the status of a persstent objector s the necessty to support a newly ndependent state s soveregnty and equalty (Vller, 1985, pp ). 6 Hosted by The Berkeley Electronc Press

9 2. The Formaton of Custom wth Persstent Objectors In the recent law and economcs lterature, attenton has been devoted to the emergence, sustanablty, and change of nternatonal customary law (Goldsmth and Posner, 1999 and 2000; Fon and Pars, 2002). Ths Secton wshes to contrbute to that lterature analyzng the mpact of the persstent objector doctrne on the process of custom formaton when heterogeneous states are nvolved. As dscussed above, customary rules emerge from past practce. Pror to the soldfcaton of a practce nto a bndng custom, states engage n actons on a purely voluntary bass, takng nto account the costs and benefts of the acton and ther nterest n establshng a customary rule that would bnd for the future. 13 After the ntal perod, from perod 1 to nfnty states alternate roles on a probablstc bass and engage n repeated nteracton. Each state confronts probablty α that once the custom s establshed, t may receve a beneft from other states complance wth the custom, and probablty β that state may be called upon to fulfll oblgatons created by the custom. 14 Consder the emergence of a multlateral custom among M heterogeneous states. A level of partcpaton effort e characterzes the content of the customary rule. 15 Effort to comply wth the custom mposes costs on the performng state and benefts on the recevng state. A state 2 that partcpates n the custom wth level of effort e faces complance costs ae and generates benefts be to other states. Once the custom s establshed, the state can rely on recprocal 13 Before practces mature nto a custom, states face a voluntary partcpaton problem smlar to that studed by Fon and Pars (2002). They nvestgated blateral custom under recprocty and dscussed the ablty of custom formaton to generate Kaldor-Hcks effcent customs. Ths paper extends those fndngs to persstent objector and subsequent objector doctrnes. 14 The nterpretaton of probabltes α and β can be llustrated by the followng example. Imagne that a customary rule mposes an affrmatve duty on coastal states to rescue foregn vessels wthn a range of 200 mles from the state s coastlne. Then α represents the probablty that state s vessels may need rescue and beneft from the customary rescue rule. Ths probablty depends on the number of vessels that fly state s flag when navgatng the hgh seas. β represents the probablty that state may be called upon to rescue other states vessels. Ths probablty depends on the extent of state s coastlne and navgaton routes n ts proxmty. 15 In our rescue example, the effort level e represents the standard of care or nvestment of resources that states undertake when rescung other states vessels under the customary practce. 7

10 conduct from other states. Assumng that the state has a dscount rate r (r > 0 ), the deal level of custom partcpaton for state s dentfed by solvng the followng problem: 16 max e 1 2 P = ( α be βae ) (1) r The deal level of custom partcpaton chosen by state s thus: e b = α, (2) 2β a and the payoff achevable under the custom for state s: 2 2 α b Pe ( ) = 4 β ar Note that f states are homogeneous, so that each state faces the same probabltes, costs, benefts, and partcpaton constrants, then the nterests of all states converge. Each state desres b the same custom level e = α, and no state has an ncentve to become a persstent objector. 2β a The presence of heterogeneous states mples that partcpatng states may have dfferent vews on the desrablty and content of the custom. The persstent objector doctrne provdes a mechansm through whch the dfferent actons and objectons of the states are brought together to generate a rule of custom. 17 When a typcal heterogeneous state chooses not to partcpate n the emergng custom, the alternatve for the state s to contnue ts undertakngs n the absence of a recognzed rule. In many nstances the no-custom regme mples adoptng a self-help approach. In the absence of custom, the state faces the cost of ts own effort each tme t seeks to obtan a beneft for tself, and the probabltes of supplyng and recevng help thus equal α. 18 (3) 16 A dscount rate reflects the state s tme preference on the uncertanty concernng the effectve emergence of a custom. See Fon and Pars (2002) for more dscusson. 17 Persstent objector states may opt out n full or n part from excessve customary oblgatons. There s no symmetrc opportunty for persstent objector states to force a level of customary oblgaton hgher than the emergng custom. Obvously, dfferences among states based on asymmetrc preferences can be settled by means of blateral or multlateral treates specfyng specfc treaty oblgatons for the states. Such talorng of nternatonal oblgatons to the needs of states s not possble under general customary law, gven the ntal need for unform customary practces. 18 For example, wth respect to our hypothetcal rescue rule, rejecton of the custom mples that the state prefers a self-help approach n whch each state faces the burden of rescung ts own shps, even when far from the state s 8 Hosted by The Berkeley Electronc Press

11 Generally speakng, we assume that the costs faced by the state n a no-custom regme are ae 2, whch dffer from costs faced by the state under the custom. 19 We assume that the beneft receved s the same and equals faced by state depends on solvng the followng problem. be. Gven these assumptons, the custom-partcpaton problem ma x P = α ( be a e ) (4) r e 1 2 The optmal choce of effort for the no-custom regme s e = b 2 a. The optmal payoff obtanable by the state n the absence of the custom s gven by the followng: b Pe ( ) = α 2 4ar (5) State s best obtanable payoff n the no-custom regme, Pe ( ), determnes state s partcpaton n the custom. State chooses to partcpate n the custom when the best obtanable payoff under the custom s hgher than Pe ( ). States may gan an exempton from customary law by persstently objectng to an emergng customary practce. Objecton can be full or partal. Objecton s full when a state s altogether unwllng to jon the custom, whatever ts content. Objecton s partal when a state s wllng to jon the custom, but prefers a level of effort lower than that requred by the emergng custom. 20 Consder the behavor of two groups of states. The frst group of states desres a lower level of oblgaton than that requred by the custom. Conversely, the other group of states prefers a hgher level of oblgaton than the emergng custom would delver. Frst, take the case n whch the deal level of custom partcpaton than the emergng custom oblgaton level e C for state s less. Should state decde to jon the custom, t would never choose full partcpaton, gven the opportunty to obtan partal exempton va the persstent objector doctrne. Ths s true because the payoff obtanable at the prvately optmal e e own coastlne, wthout the assstance of other states n closer proxmty to the accdent. Under the self-help regme, states must assst ther own vessels each tme they are n trouble. 19 Ths can be easly understood n the rescue example. The cost of rescung a shp far from the state s coastlne s dfferent from the cost to the state of rescung a foregn vessel n the proxmty of ts coast. 20 As a second-best soluton, n the face of a persstent objecton, other states take advantage of the recprocal effects of a unlateral objecton, allowng them to adopt the same customary level aganst the objectng state. In ths context, the persstent objector doctrne consttutes an example of weak recprocty studed n Fon and Pars (2003). 9

12 s hgher than that obtaned by full adherence to the custom. Thus, state ether jons the custom partally by becomng a partal persstent objector, or opts out of the custom altogether by rasng full objecton. In ether case, state takes advantage of the opportunty to be a persstent objector. The choce between full and partal objecton s drven by the relatve magntudes of Pe ( ) and Pe ( ). If Pe ( ) s greater than Pe ( ), the payoff under the no-custom regme s hgher than the payoff from jonng the custom. State Substtutng the values found n (3) and (5) for state fully objects f 1 a small and/or the probablty rato α Pe ( ) and e C therefore fully objects to the custom. Pe ( ) and smplfyng, we see that > α. Thus, when the cost of not jonng the custom a s relatvely β a β s small, the persstent objector state fully opposes the emergng custom. 21 On the other hand, when the cost of not jonng the custom s rather large and/or the probablty rato α emergng custom. β s large, the persstent objector state partally opposes the C greater than the emergng custom oblgaton level e. Although state custom s gven by the payoff at the custom oblgaton level e C : Pe ( C ). The partcpaton C C Pe ( ) and Pe ( ). If Pe ( ) s greater than Pe ( ), there s full partcpaton n the custom and Next, consder the case n whch the deal level of custom partcpaton for state s prefers the emergence of a custom wth a hgher level of oblgaton, persstent objector states cannot force a level of customary oblgaton hgher than the emergng custom. Thus, the state s beneft from jonng the constrant now requres a comparson between the payoff obtaned under the no-custom regme state does not become a persstent objector. If Pe) C ( s greater than Pe ( ), state s better off optng out of the custom altogether by becomng a full persstent objector. The above analyss brngs to lght some nterestng results. Frst, dfferent categores of states may choose to opt out of an emergng custom. Full objecton s a ratonal strategy not only for states that consder the emergng custom excessvely burdensome, but also for states that lke e 21 If the probablty rato of recevng beneft and performng under custom α β s small, state s less lkely to receve a beneft than to face the burden of future mplementaton of the custom. State can be consdered a low beneft or hgh cost state. Thus, n ths case t s more lkely for state to fully oppose the custom. 10 Hosted by The Berkeley Electronc Press

13 the custom but want more of t. Some states agree wth the sprt of the custom but are not satsfed wth the emergng rule because they would lke a custom wth a greater level of oblgaton. Some of these states may be better off optng for a no-custom regme and addressng the ssue on ther own. The payoff n a no-custom regme represents the opportunty cost of custom partcpaton dentfed n (5). Ths opportunty cost wll lkely be larger for stronger states that face lower cost, a, and whch may have greater opportuntes to stand alone and generate benefts for themselves n the absence of nternatonal cooperaton. For those states customary cooperaton s less ndspensable than for other states that have less opportunty to address the underlyng need by actng on ther own. Gven the lower payoff obtanable n a nocustom regme, weaker states facng hgher costs may be more wllng to go along wth an emergng custom that does not correspond to ther deal level. Second, the lkelhood of partcpaton n a less than deal custom depends on the rato of the probabltes of beng on the recevng sde versus the gvng sde of the customary relatonshp n future tme perods. States that are more lkely to beneft from the custom than to be burdened by t are more lkely to partcpate n the custom, even though the custom does not correspond to ther deal optmum. Fnally, the level of objecton would dffer f states had to formulate objectons at the tme they were called upon to comply wth the custom. In ths model we do not nclude the ntal cost of custom complance because the persstent objector doctrne requres the objecton to be consstent (.e., states objectons should be formulated ex ante, rather than when states are called upon to perform a custom oblgaton). The legal requrement of consstency s thus nstrumental to avod manpulaton of the content of the custom by a state s myopc strategc objecton. If allowed to formulate objectons when complance s due, states mght be tempted to corrode the mutual long-term benefts of the custom to avod mmedate complance costs. Ths would compromse the ablty of the custom process to generate desrable levels of legal oblgatons. 11

14 3. Subsequent Objector Doctrnes n Internatonal Customary Law Accordng to tradtonal nternatonal law, states can object to a norm of nternatonal customary law only durng ts emergence. The persstent objector doctrne requres a tmely reacton of states to emergng customs. If a state wats to object untl after the practce becomes a bndng rule of nternatonal customary law, the state cannot clam exempton from t. Subsequent departures of a state from an establshed custom would consttute an nternatonal wrong, unless other states acquesce to the state s late departure. A state cannot unlaterally depart from a customary rule once t has become bound by t. 22 Ths tradtonal approach provdes an opt-out opportunty durng the formatve phase of a custom but provdes no flexblty for subsequent adaptaton of custom to the changng needs of the nternatonal communty over tme. In the context of multlateral customs, nternatonal law practce has gradually developed doctrnes to avod excessve rgdty of nternatonal customary law. One such doctrne, resultng from the applcaton of the long-standng prncple of rebus sc stantbus to customary law, allows states to depart from nternatonal law n the face of fundamental changes n the state of affars that led to the orgnal legal oblgaton (Kontou, 1994). 23 Gven ther lmted verfablty, changes to ndvdual states costs and benefts are not covered by the rebus sc stantbus prncple. Lkewse, states are not allowed to nvoke changes n nternal laws or polces as a justfcaton for a unlateral departure from nternatonal customary law. 24 Departures from customary law that are not supported by the rebus sc stantbus prncple may nevertheless fnd lmted accommodaton n the subsequent objector doctrne (Brownle, 1990). The subsequent objector doctrne addresses stuatons where a state (the subsequent objector state) objects or departs from a customary rule after ts formaton, as opposed to 22 See Wolfke (1993, p. 66) A state may certanly not unlaterally at wll refuse the legal consequences of ts prevous consent to accept a practce as law The rebus sc stantbus prncple s often referred to as the law of changed crcumstances. It allows a state to termnate an exstng oblgaton on the grounds of fundamental and unforeseen changes n crcumstances, as long as the changes were not caused by the state nvokng the excuse (Brownle, 1990). 24 A fundamental change n crcumstances may be the bass of an exempton from nternatonal law only f t ncreases the burden of the oblgatons to be executed to the extent of renderng the performance somethng essentally dfferent from that orgnally undertaken. Fsheres Jursdcton Case (1973). 12 Hosted by The Berkeley Electronc Press

15 objectng to the rule durng ts emergence, as n the persstent objector case. 25 The effects of a state s departure from a prevously recognzed custom are determned by the speed and spread of the process of defecton. Many dfferent outcomes are possble under ths doctrne. One lmtng case occurs f a substantal number of states depart from an old custom. If the momentum of wdespread defecton s accompaned by general acquescence by the remanng states, a new rule may result. Thus f events unfold rapdly, one state s departure from an exstng custom may trgger the emergence and wdespread adopton of a new custom. The other lmtng takes place when the subsequent objector s departure from customary law s met wth general opposton by other states. In ths case the subsequent objector s acton, far from generatng a new custom, s construed as a breach of nternatonal customary law. The subsequent objector doctrne n fact does not allow unlateral departures from exstng custom. The subsequent objector doctrne provdes rules to govern the array of possbltes contaned between these lmtng cases. Specfcally, when defecton s not wdespread and t s not possble to dentfy a new emergng general custom, the effects of the subsequent objector s actons depend on specfc relatonshps wth the opposng states. The subsequent objector doctrne specfes that n the face of a unlateral departure from an exstng custom, a subsequent objector can only gan an exempton from a rule of customary law f, and to the extent that, ts departure s not opposed by other states. Snce the reactons of the other states may dffer from one another, applcaton of the subsequent objector doctrne leads to the creaton of a network of specal relatons based on opposablty, acquescence, and hstorc ttle (Brownle, 1990, p. 5). For example, the relatonshp between a subsequent objector and a fully acquescng state s governed by a blateral oblgaton consstent wth the norm advocated by the objector state. The relatonshp between a subsequent objector and an opposng state remans governed by the preexstng custom. Fnally, when the departure s only partally opposed, the content of the rule governng the blateral relaton between the departng state and the partally objectng state changes accordng to the extent of the latter state s acquescence. 25 Vllger (1985, p. 17) dscusses the dffcultes n recognzng subsequent objectors unlateral departures and the need to obtan acquescence from other states: Ther poston s untenable, n part, because other states have come to rely on the subsequent objector orgnally conformng to the rule. Also, general customary law s bndng on all states and cannot, n the words of the Court, be subject of any rght of unlateral excluson exercsable at wll by any one of [the nternatonal communty members] n ts own favor. (Quotng North Sea Cases ICJ Reports 1969). See also Sten (1985, p. 458). 13

16 The above process mples that when one state departs from a preexstng custom and another state acquesces to such departure the subsequent objector doctrne allows the rule to be modfed between these partes. 26 The change n customary law affects only the relatons between these states. Other states must choose between becomng partes to a new or amended custom that may affect ther rghts under the preexstng customary rule, or contnue to adhere to the old regme and demand complance wth the preexstng custom by the departng state. Even n the face of a thrd state s opposton, the change n the customary law between the departng state and the acquescng state wll take place. 27 In practce, ths process often fragments a prevously unform rule of custom nto a network of blateral relatons, where the content of each blateral relaton s determned by the extent of one state s departure and the other state s acquescence Custom wth Subsequent Objectors: Theoretcal Consderatons In the subsequent objector doctrne, the objecton to a custom takes the form of a departure from an establshed and already bndng rule of custom. To hghlght and separate the subsequent objector s problem from the persstent objector s problem, we start wth a group of 26 Ths process bears some smlarty wth the rules governng the amendment of nternatonal treaty law. Under 334 (3) of the Restatement of the Law, Thrd Foregn Relatons Law of the Unted States: 334. Amendment or Modfcaton of Internatonal Agreement. (1) An nternatonal agreement may be amended by agreement between the partes. [ ] (3) Two or more of the partes to a multlateral agreement may agree to modfy the agreement as between themselves alone f such modfcaton [ ] would not be ncompatble wth the rghts of the other partes to the agreement or wth ts object and purpose. Under ths provson, an amendment s permssble and takes effect for the states that agree to t even f other states do not agree to the amendment. See also 1969 Venna Conventon on the Law of Treates, Artcle 41(2). 27 The change n customary law takes effect for the departng states and the states that provde mplct consent va acquescence unless the rule of customary law s one of jus cogens or the change to the two states practce adversely affects the nterests of thrd party states. 28 Note however that whle a subset of states can modfy the effects of a customary rule by subsequent practce or modfy a treaty oblgaton by subsequent treaty amendment, nternatonal law s stll ambvalent on the ssue of modfcaton of treates va subsequent practce. The Internatonal Law Commsson proposed an artcle provdng that a treaty could be modfed by subsequent practce ndcatng agreement to such modfcaton. As explaned n the Reporter s Notes to the Restatement of the Law, Thrd Foregn Relatons Law of the Unted States, that proposal was deleted after the delegaton of the Unted States, among others, objected that an agreement mght be deemed amended as a result of unauthorzed actons by state offcals. Kearney and Dalton (1970, p. 525). The queston of modfcaton by subsequent practce tends to merge nto that of nterpretaton by subsequent practce under 325, Comment c. See also Decson of Arbtraton Trbunal concernng Internatonal Ar Transport Servces Agreement between France and the Unted States, 16 R.Int'l Arb. Awards 5 (1964). 14 Hosted by The Berkeley Electronc Press

17 homogeneous states actng under an establshed custom. Ths stylzed smplfcaton ensures that when the custom emerges, no state has an ncentve to become a persstent objector. In partcular, each state faces the same probablty of recevng beneft α, the probablty of beng burdened by the custom oblgaton β, the same dscount rate r, and the same beneft and cost from partcpaton n the custom, be and ae 2. Thus, each homogeneous state s confronted wth the forward-lookng problem before the practce consoldates to a custom: ma x P = ( αbe βae ), (6) r e 1 2 and each state chooses the followng effort level: b e * = α. (7) 2a β Gven homogenety of the states, the effort level respectve oblgatons under customary law. * e characterzes the content of the states Gven an exstng rule of customary law, there are many reasons why a state may become a subsequent objector. 29 Some reasons are merely strategc: a state may object to an exstng rule of customary law to avod the cost of fulfllng ts oblgatons under that rule. Other subsequent objectons are drven by changes n the costs and benefts of the custom. For example, f the cost a of complyng wth the custom has ncreased or f the probablty α of recevng a beneft from other states complance has decreased, a state may develop dfferent vews on the desrable content of the custom. 30 To understand how other states react to a subsequent objector s departure from exstng custom, t s useful to separate states nto three groups. The frst group conssts of frst-party states that have reasons to become subsequent objector states. The second group of states comprses second-party states that would beneft from the subsequent objector s fulfllment of the customary oblgaton. Fnally, thrd-party states nether expend effort to fulfll the customary oblgaton nor receve any drect beneft from the subsequent objector s complance n the current perod. 29 Unlke persstent objectors who rase objectons pror to facng a complance problem when the custom s not yet bndng, subsequent objectors manfest ther objectons by departng from an already bndng rule of customary law. 30 Ths can be seen from (7). 15

18 Just as a state may become a subsequent objector for varous reasons, dfferent factors nfluence the reactons of second-, thrd-, and other frst-party states to a proposed departure of a subsequent objector. 31 We frst consder the case of no exogenous changes n the crcumstances of all states. Then we assume unform changes n the crcumstances of all states. Fnally, we study the subsequent objector doctrne gven asymmetrc changes n the crcumstances of all states. 4.1 Strategc departures, subsequent objector doctrne, and opposton from other states Consder the case n whch probabltes, benefts and costs assocated wth the expected long-term partcpaton n the custom do not change for any state. A frst-party state may stll become a subsequent objector for strategc and myopc reasons. In one perod, the frst-party state confronts ts turn to fulfll the oblgatons under customary law. The need to ncur an mmedate cost for complance wth the custom may nduce the frst-party state to nvoke a standard dfferent from the exstng customary law and to become a subsequent objector. Due to the mmedate performance costs the frst-party state faces a somewhat dfferent yet myopc problem from before: 2 max P1 = ae + ( αbe βae ). (8) e r 2 1 The prvately optmal effort of the frst-party state now dffers from the exstng customary oblgaton: e 1 α b = 2ar ( + β). (9) Snce α α <, from (9) and (7) we see that e1 e. The frst-party state wshes to ( r + β) β < * depart from the exstng rule of custom and s wllng to lower the future customary oblgatons for all partcpants n lght of ts current stuaton. Although e 1 s frst-best for the subsequent 31 Other frst-party states that become subsequent objectors also react to the orgnal subsequent objector state. The content of the custom between two frst-party states who both want to depart from the exstng custom, perhaps to dfferent levels, s governed by the subsequent objector doctrne n ways smlar to those explctly consdered n ths secton. 16 Hosted by The Berkeley Electronc Press

19 objector state, any value less than the orgnal customary rule greater than e 1 * s better than e, as long as t s. Thus, n proposng a departure from the exstng custom, the subsequent objector effectvely puts a lower bound on the acceptable level of custom at e. If the subsequent objector state could have ts own way, custom would evolve to a lower level, wth a partal eroson of the preexstng customary rule. But the subsequent objector s proposed departure s not necessarly acceptable to other states. 32 When another state does not oppose (acquescence) the subsequent objector s departure from an exstng custom, the content of the custom changes from the orgnal value * e * to e for both the subsequent objector and the e * 1 acquescng states. When another state opposes (no acquescence) the subsequent objector s departure from an exstng custom, the content of the custom between the subsequent objector and the non-acquescng state remans at the orgnal value e 1. In the ntermedate case n whch departure s partally opposed (partal acquescence), the content of the custom between the two * states changes from the orgnal customary value e to the lower value acquesced by the other state. A typcal thrd-party state acquesces to the frst-party state s departure from an exstng custom only f the resultng change to the custom yelds a total payoff that exceeds the payoff obtanable under the current rule. Snce there s no oblgaton to comply n the current perod, there are no mmedate benefts to be ganed, and no change occurred, the thrd-party state s problem does not change. That s, the problem confrontng the thrd-party state s agan gven n (6) and the exstng customary level of effort gven n (7) remans optmal to the thrd-party state. The thrd-party state contnues to fnd the exstng custom oblgaton prvately optmal: e = 3 e *. (10) Ths means that n the absence of changes to the exogenous varables, a thrd-party state opposes the subsequent objector state s departure. Smlar to a thrd-party state, a second-party state acquesces to another state s departure from an exstng custom only f the resultng change n custom yelds a total payoff at least as large as the payoff obtanable under the current custom. Although there are no changes to the 32 Unlke persstent objectors who can gan an exempton from an emergng custom by unlaterally objectng, subsequent objectors can only gan an exempton from a rule of customary law f ther departure from an exstng custom s not opposed by other states. 17

20 crcumstances of the second-party state, ths state derves an mmedate beneft from the subsequent objector s fulfllment of the customary oblgaton n the current perod. Thus, the problem confrontng the second-party state s no longer gven by (6). Instead, t s the followng: 1 2 ma x P2 = be+ ( αbe βae ). (11) e r Ths means that the desred custom for the thrd-party state s characterzed by effort level: e 2 ( r+ α)b = 2a β. (12) Gven the expectaton of an mmedate beneft from the other state s complance wth the custom, the second-party state desres a level of effort e that s larger than the one requred by exstng customary law state s departure to a level lower than e *. 2 b e * = α. The second-party state opposes the subsequent objector 2a β Affected by strategc and myopc consderatons, a second-party state opposes more strongly an objector s departure than does a neutral thrd-party bystander, as can be seen from the fact that e > * 2 e = e. These results suggest that n the absence of any change n crcumstances for all states, the subsequent objector doctrne effectvely constrans departures from exstng customary law drven solely by the attempt to avod mmedate costs of complance. Any such strategc attempts to depart are always met wth opposton by second- and thrd-party states Strategc non-acquescence and the nerta of customary law After the formaton of a custom, there may be changes to exogenous factors affectng the behavor of states. We next concentrate on a unform change to all states that gves the frstparty state an addtonal reason to depart from the custom. Wthout loss of generalty, assume that the cost of performng ncreases from a to a for all states. Updatng the problem confrontng the frst-party state and adjustng the effort level from (9), the frst-party state now 18 Hosted by The Berkeley Electronc Press

21 chooses to depart from the exstng customary level e * to effort level e where e satsfes the followng: α b e = < e < e * 1 1. (13) 2a ( r+ β) In addton to the mmedate complance cost ssue, the frst-party state now ncurs a hgher cost to fulfll ts oblgatons under the custom. Ths provdes an addtonal reason for the frst-party state to become a subsequent objector. 34 Indeed, comparng effort level for ths case and effort level e n (9) when there are no exogenous changes n performance cost, the frst-party 1 state now has an ncentve to depart from the custom by adoptng a lower level than t would adopt n the absence of an ncrease n performance cost. Gven the rse n performance cost, the thrd-party state s also nclned to adopt a lower level of custom than before. Updatng the optmal level of effort n (7), the thrd-party state now desres e where 3 α b e1 < e3 = < e *. (14) 2a β Thus, nduced by hgher cost the thrd-party state consents to a change n custom by partally acquescng to e. The customary oblgatons of two states towards one another can only be modfed by the extent to whch both mplctly agree to the change. Partal acquescence by the thrd-party state to the subsequent objector therefore leads to a partal change n customary law. The content of the custom between the two states changes from the orgnal customary value e to e. 3 3 For the second-party state, the problem s smlar to that consdered prevously, wth an mmedate beneft term. Ths tme however the second-party state faces the same exogenous cost change faced by the other states. Adjustng (12) to the hgher cost parameter a, the optmal level of effort for the second-party state becomes: e 1 * 33 In the presence of unform exogenous changes to the states, optmal effort levels are denoted wth a prme. 34 Naturally, a unform change for all states can have a mtgatng effect on the subsequent objector s departure. For example, f the cost of performng has decreased, the frst-party state s nduced to undertake a hgher level of effort. Ths counteracts the need for the frst-party state to mnmze the effort level to reduce the mmedate burden of complance. Lkewse, the decrease n cost also has dfferent mpacts on second- and thrd-party states. We concentrate on the case where t s more lkely for the exstng custom to erode. 19

22 ( r+ α) b e2 = 2a β (15) b Comparng the level of effort n (15) wth the exstng customary level e * = α, t s not clear 2a β whether e 2 * or e s larger; the mmedate beneft has a postve mpact on the level of effort whle the ncrease n future performance cost has a negatve mpact. When e s greater than or equal to e *, the second-party state opposes the subsequent objector s departure. Ths prevents any change n the custom governng the relatonshp between the frst- and second-party state. When e 2 s less than e *, gven that e 2 n (15) s greater than e 1 n (13), the second-party state only partally opposes the subsequent objector s departure. Hence, the content of the custom * between the two states changes from the orgnal customary value e to To conclude, when all states face a unform ncrease n performance cost, there s a partal convergence of nterests between the subsequent objector and the thrd-party state. The subsequent objector s departure from the current custom s motvated by the attempt to reduce the burden of mmedate complance and to mnmze the mpact of hgher complance costs n the future. The thrd-party state shares the motve to reduce the mpact of hgher complance costs n the future. Thus the subsequent objector has ncentves to depart more extensvely from the exstng custom than the thrd-party state would lkely allow. For the second-party state, the net effect of an exogenous change n costs depends on whether the presence of an mmedate beneft for the second-party state s offset by the ncrease n future performance cost. If the mpact of mmedate beneft domnates, the second-party state s ether content wth the current customary rule or wants a level of custom hgher than the current level. The second-party state opposes any departure by the subsequent objector from the current custom, and the relatonshp between the two states remans governed by the exstng customary rule. If the mpact nduced by the ncrease n future performance cost domnates, the second-party state s prvate optmum falls below the exstng customary law. Stll, the secondparty state s prvate optmum s greater than the level preferred by the subsequent objector. In ths case a partal convergence between the nterests of the subsequent objector state and the second-party state takes place. The second-party state foregoes part of the mmedate beneft e Hosted by The Berkeley Electronc Press