## 1. General Issues



Social norms, like many other social phenomena, are the unplanned
result of individuals' interaction. It has been argued that
social norms ought to be understood as a kind of grammar of social
interactions. Like a grammar, a system of norms specifies what is
acceptable and what is not in a society or group. And, analogously to
a grammar, it is not the product of human design. This view suggests
that a study of the conditions under which norms come into
being--as opposed to one stressing the functions fulfilled by
social norms--is important to understand the differences between
social norms and other types of injunction (such as hypothetical
imperatives, moral codes, or legal rules).



Another important issue often blurred in the literature on norms is
the relationship between normative beliefs and behavior. Some authors
identify norms with observable, recurrent patterns of behavior. Others
only focus on normative beliefs and expectations. Such accounts find
it difficult to explain the complexity and heterogeneity of
norm-driven behaviors, as they offer an explanation of conformity that
is at best partial.



Some popular accounts of why social norms exist are the following.
Norms are efficient means to achieve social welfare (Arrow 1971;
Akerlof 1976), prevent market failures (Jules Coleman 1989), or cut
social costs (Thibaut & Kelley 1959; Homans 1961); norms are
either Nash equilibria of coordination games or cooperative equilibria
of prisoner's dilemma-type games (Lewis 1969; Ullmann-Margalit
1977), and as such they solve collective action problems.



Akerlof's (1976) analysis of the norms that regulate land
systems is a good example of the tenet that "norms are efficient
means to achieve social welfare". Since the worker is much
poorer and less liquid than the landlord, it would be more natural for
the landlord rather than the tenant to bear the risk of crop failure.
This would be the case if the landlord kept all the crops, and paid
the worker a wage (i.e., the case of a "wage system").
Since the wage would not directly depend on the worker's effort,
this system leaves no incentive to the worker for any effort beyond
the minimum necessary. In sharecropping, on the contrary, the worker
is paid both for the effort and the time he puts in: a more efficient
arrangement in that it increases production.



Thibaut and Kelley's (1959) view of norms as substitutes for
informal influence has a similar functionalist flavor. As an example,
they consider a repeated battle of the sexes game. In this game, some
bargaining is necessary for each party to obtain, at least
occasionally, the preferred outcome. The parties can engage in a
costly sequence of threats and promises, but it seems better to agree
beforehand on a rule of behavior, such as alternating between the
respectively preferred outcomes. Rules emerge because they reduce the
costs involved in face-to-face personal influence.



Likewise, Ullman-Margalit (1977) uses game theory to show that norms
solve collective action problems, such as prisoner's
dilemma-type situations; in her own words, "... a norm
solving the problem inherent in a situation of this type is generated
by it" (1977: 22). In a collective action problem, self-centered
rational choices produce a Pareto-inefficient outcome.
Pareto-efficiency is restored by means of norms backed by sanctions.
James Coleman (1990), too, believes that norms emerge in situations in
which there are externalities, that is, in all those cases in which an
activity produces negative (positive) effects on other parties,
without this being reflected in direct compensation; thus the producer
of the externality pays no cost for (reaps no benefit from) the
unintended effect of their activity. A norm solves the problem by
regulating the externality-producing activity, introducing a system of
sanctions (rewards).



Also Brennan, Eriksson, Goodin, and Southwood (2013) argue that norms
have a function. Norms function to hold us accountable to each other
for adherence to the principles that they cover. This may or may not
create effective coordination over any given principle, but they place
us in positions where we may praise and blame people for their
behaviors and attitudes. This function of accountability, they argue,
can help create another role for norms, which is imbuing practices
with social meaning. This social meaning arises from the expectations
that we can place on each other for compliance, and the fact that
those behaviors can come to represent shared values, and even a sense
of shared identity. This functional role of norms separates it from
bare social practices or even common sets of desires, as those
non-normative behaviors don't carry with them the social
accountability that is inherent in norms. The distinctive feature of
the Brennan et al. account of norms is the centrality of
accountability: this feature is what distinguishes norms from other
social practices.



All of the above are examples of a *functionalist* explanation
of norms. Functionalist accounts are sometimes criticized for offering
a post hoc justification for the existence of norms (i.e., the mere
presence of a norm does not justify inferring that that norm exists to
accomplish some social function). Indeed, a purely functionalist view
may not account for the fact that many social norms are harmful or
inefficient (e.g., discriminatory norms against women and minorities),
or are so rigid as to prevent the fine-tuning that would be necessary
to accommodate new cases. There, one would expect increasing social
pressure to abandon such norms.



According to some authors, we can explain the emergence of norms
without any reference to the functions they eventually come to
perform. Since the norms that are most interesting to study are those
that emerge naturally from individuals' interactions (Schelling
1978), an important theoretical task is to analyze the conditions
under which such norms come into being. Because norms often provide a
solution to the problem of maintaining social order--and social
order requires cooperation--many studies on the *emergence and
dynamics* of norms have focused on cooperation. Norms of honesty,
loyalty, reciprocity and promise-keeping are indeed important to the
smooth functioning of social groups. One hypothesis is that such
cooperative norms emerge in close-knit groups where people have
ongoing interactions with each other (Hardin 1982). Evolutionary game
theory provides a useful framework for investigating this hypothesis,
since repeated games serve as a simple approximation of life in a
close-knit group (Axelrod 1984, 1986; Skyrms 1996; Gintis 2000). In
repeated encounters people have an opportunity to learn from each
other's behavior, and to secure a pattern of reciprocity that
minimizes the likelihood of misperception. In this regard, it has been
argued that the cooperative norms likely to develop in close-knit
groups are simple ones (Alexander 2000, 2005, 2007); in fact, delayed
and disproportionate punishment, as well as belated rewards, are often
difficult to understand and hence ineffective. Although norms
originate in small, close-knit groups, they often spread well beyond
the narrow boundaries of the original group. The challenge thus
becomes one of explaining the dynamics of the norm propagation from
small groups to large populations.



If norms can thrive and spread, they can also die out. A poorly
understood phenomenon is the sudden and unexpected *change of
well-established patterns* of behavior. For example, smoking in
public without asking for permission has become unacceptable, and only
a few years ago nobody would have worried about using gender-laden
language. One would expect inefficient norms (such as discriminatory
norms against women and minorities) to disappear more rapidly and with
greater frequency than more efficient norms. However, Bicchieri (2016)
points out that inefficiency is not a sufficient condition for a
norm's demise. This can be seen by the study of crime and
corruption: corruption results in huge social costs, but such
costs--even when they take a society to the brink of
collapse--are not enough to generate an overhaul of the system.
Muldoon (2018a, 2018b, 2020) has argued that social norms are a
challenging form of social regulation precisely because there is no
simple way to intentionally modify a social norm, as one can with a
law or institutional rule. Social norms can even shape one's
understanding of how much agency one has (Muldoon 2017).



An influential view of norms considers them as clusters of
self-fulfilling expectations (Schelling 1960), in that some
expectations often result in behavior that reinforces them. A related
view emphasizes the importance of *conditional preferences* in
supporting social norms (Sugden 2000). In particular, according to
Bicchieri's (2006) account, preferences for conformity to social
norms are conditional on "empirical expectations" (i.e.,
first-order beliefs that a certain behavior will be followed) as well
as "normative expectations" (i.e., second-order beliefs
that a certain behavior ought to be followed). Thus, norm compliance
results from the joint presence of a conditional preference for
conformity and the belief that other people will conform as well as
approve of conformity.



Note that characterizing norms simply as clusters of expectations
might be misleading; similarly, a norm cannot simply be identified
with a recurrent behavioral pattern either. If we were to adopt a
purely behavioral account of norms there would be no way to
distinguish shared rules of fairness from, say, the collective morning
habit of tooth brushing. After all, such a practice does not depend on
whether one expects others to do the same; however, one would not even
try to ask for a salary proportionate to one's education, if one
expected compensation to merely follow a seniority rule. In fact,
there are behavioral patterns that can only be explained by the
existence of norms, even if the behavior prescribed by the norm in
question is currently unobserved. For example, in a study of the Ik
people, Turnbull (1972) reported that starved hunters-gatherers tried
hard to avoid situations where their compliance with norms of
reciprocity was expected. Thus they would go out of their way not to
be in the position of gift-taker, and hunted alone so that they would
not be forced to share their prey with anyone else. Much of the
Ik's behavior could be explained as a way of eluding existing
reciprocity norms.



There are many other instances of *discrepancies between
expectations and behavior*. For example, it is remarkable to
observe how often people expect others to act selfishly, even when
they are prepared to act altruistically themselves (Miller &
Ratner 1996). Studies have shown that people's willingness to
give blood is not altered by monetary incentives, but typically those
very people who are willing to donate blood for free expect others to
donate blood only in the presence of monetary rewards. Similarly, all
the interviewed landlords answered positively to a question about
whether they would rent an apartment to an unmarried couple; however,
they estimated that only 50% of other landlords would accept unmarried
couples as tenants (Dawes 1972). Such cases of pluralistic ignorance
are rather common; what is puzzling is that people may expect a given
norm to be upheld in the face of personal evidence to the contrary
(Bicchieri & Fukui 1999). Furthermore, there is evidence
suggesting that people who donate blood, tip on a foreign trip, give
money to beggars or return a lost wallet often attempt to downplay
their altruistic behavior (by supplying selfish motives that seemingly
align their actions with a norm of self-interest; Wuthnow 1991, 77).



In a nutshell, norms refer to actions over which people have control,
and are supported by shared expectations about what should or should
not be done in different types of social situations. However, norms
cannot be identified just with observable behavior, nor can they
merely be equated with normative beliefs.



The varying degrees of correlation between normative beliefs and
actions are an important factor researchers can use to differentiate
among various types of norms. Such a correlation is also a key element
to consider when critically assessing competing theories of norms: we
begin by surveying the socialized actor theory, the social identity
theory, and some early rational choice (cost-benefit) models of
conformity.


## 2. Early Theories: Socialization



In the theory of the socialized actor (Parsons 1951), individual
action is intended as a choice among alternatives. Human action is
understood within a utilitarian framework as instrumentally oriented
and utility maximizing. Although a utilitarian setting does not
necessarily imply a view of human motives as essentially egoistic,
this is the preferred interpretation of utilitarianism adopted by
Talcott Parsons and much contemporary sociology. In this context, it
becomes crucial to explain through which mechanisms social order and
stability are attained in a society that would otherwise be in a
permanent Hobbesian state of nature. In short, order and stability are
essentially socially derived phenomena, brought about by a *common
value system*--the "cement" of society. The
common values of a society are embodied in norms that, when conformed
to, guarantee the orderly functioning and reproduction of the social
system. In the Parsonian framework norms are exogenous: how such a
common value system is created and how it may change are issues left
unexplored. The most important question is rather how norms get to be
followed, and what prompts rational egoists to abide by them. The
answer given by the theory of the socialized actor is that people
voluntarily adhere to the shared value system, because it is
introjected to form a constitutive element of the personality itself
(Parsons 1951).



In Parsons' own words, a norm is



> 
> 
> a verbal description of a concrete course of action, ... ,
> regarded as desirable, combined with an injunction to make certain
> future actions conform to this course. (1937: 75)
> 
> 
> 



Norms play a crucial role in individual choice since--by shaping
individual needs and preferences--they serve as criteria for
selecting among alternatives. Such criteria are shared by a given
community and embody a common value system. People may choose what
they prefer, but what they prefer in turn conforms to social
expectations: norms influence behavior because, through a process of
socialization that starts in infancy, they become part of one's
motives for action. Conformity to standing norms is a stable, acquired
disposition that is independent of the consequences of conforming.
Such lasting dispositions are formed by long-term interactions with
significant others (e.g., one's parents): through repeated
socialization, individuals come to learn and internalize the common
values embodied in the norms. Internalization is conceived as the
process by which people develop a psychological need or motive to
conform to a set of shared norms. When norms are internalized
norm-abiding behavior will be perceived as good or appropriate, and
people will typically feel guilt or shame at the prospect of behaving
in a deviant way. If internalization is successful external sanctions
will play no role in eliciting conformity and, since individuals are
motivated to conform, it follows that normative beliefs and actions
will be consistent.



Although Parsons' analysis of social systems starts with a
theory of individual action, he views social actors as behaving
according to roles that define their identities and actions (through
socialization and internalization). The goal of individual action is
to maximize satisfaction. The potential conflict between individual
desires and collective goals is resolved by characterizing the common
value system as one that precedes and constrains the social actor. The
price of this solution is the disappearance of the individual actor as
the basic unit of analysis. Insofar as individuals are role-bearers,
in Parsons' theory it is social entities that act: entities that
are completely detached from the individual actions that created them.
This consideration forms the basis for most of the criticisms raised
against the theory of the socialized actor (Wrong 1961); such
criticisms are typically somewhat abstract as they are cast in the
framework of the holism/individualism controversy.



On the other hand, one may easily verify whether empirical predictions
drawn from the socialized actor theory are supported by experimental
evidence. For instance, the following predictions can be derived from
the theory and easily put to test. (a) Norms will change very slowly
and only through intensive social interaction. (b) Normative beliefs
are positively correlated to actions; whenever such beliefs change,
behavior will follow. (c) If a norm is successfully internalized,
expectations of others' conformity will have no effect on an
individual's choice to conform.



Some of the above statements are not supported by empirical evidence
from social psychology. For example, it has been shown that there may
not be a relation between people's normative beliefs (or
attitudes) and what people in fact do. In this respect, it should be
noted that experimental psychologists have generally focused on
"attitudes", that is, "evaluative feelings of pro or
con, favorable or unfavorable, with regard to particular
objects" (where the objects may be "concrete
representations of things or actions, or abstract concepts";
Insko & Schopler 1967: 361-362). As such, the concept of
attitude is quite broad: it includes normative beliefs, as well as
personal opinions and preferences. That said, a series of field
experiments has provided evidence contrary to the assumption that
attitudes and behaviors are closely related. LaPiere (1934) famously
reported a sharp divergence between the widespread anti-Chinese
attitudes in the United States and the tolerant behavior he witnessed.
Other studies have pointed to inconsistencies between an
individual's stated normative beliefs and her actions (Wicker
1969): several reasons may account for such a discrepancy. For
example, studies of racial prejudice indicate that normative beliefs
are more likely to determine behavior in long-lasting relationships,
and least likely to determine behavior in the transient situations
typical of experimental studies (Harding et al. 1954 [1969]; Gaertner
& Dovidio 1986). Warner and DeFleur (1969) reported that the main
variable affecting discriminatory behavior is one's belief about
what *society* (e.g., most other people) says one should do, as
opposed to what one *personally* thinks one should do.



In brief, the social psychology literature provides mixed evidence in
support of the claim that an individual's normative beliefs and
attitudes influence her actions. Such studies, however, do not
carefully discriminate among various types of normative beliefs. In
particular, one should distinguish between "personal normative
beliefs" (i.e., beliefs that a certain behavior ought to be
followed) and "normative expectations" (i.e., what one
believes others believe ought to be done, that is, a second-order
belief): it then becomes apparent that oftentimes only such
second-order beliefs affect behavior.



The above constitutes an important criticism of the socialized actor
theory. According to Parsons, once a norm is internalized, members of
society are motivated to conform by an internal sanctioning system;
therefore, one should observe a high correlation among all orders of
normative beliefs *and* behavior. However, experimental
evidence does not support such a view (see also: Fishbein 1967;
Cialdini et al. 1991). Another indication that the socialized actor
theory lacks generality is the observation that norms can change
rather quickly, and that new norms often emerge in a short period of
time among complete strangers (Mackie 1996). Long-term or close
interactions do not seem to be necessary for someone to acquire a
given normative disposition, as is testified by the relative ease with
which individuals learn new norms when they change status or group
(e.g., from single to married, from student to faculty, etc.).
Moreover, studies of emergent social and political groups have shown
that new norms may form rather rapidly, and that the demise of old
patterns of behavior is often abrupt (Robinson 1932; Klassen et al.
1989; Prentice & Miller 1993; Matza 1964). Given the
aforementioned limitations, Parsons' theory might perhaps be
taken as an explanation of a particular conception of moral norms (in
the sense of internalized, unconditional imperatives), but it cannot
be viewed as a general theory of *social* norms.


## 3. Early Theories: Social Identity



It has been argued that behavior is often closely embedded in a
network of personal relations, and that a theory of norms should not
leave the specific social context out of consideration (Granovetter
1985). Critics of the socialized actor theory have called for an
alternative conception of norms that may account for the often weak
relation between beliefs and behavior (Deutscher 1973). This
alternative approach takes social relations to be crucial in
explaining social action, and considers social identity as a key
motivating factor. (A strong support for this view among
anthropologists is to be found in the work of Cancian 1975.)



Since the notion of social identity is inextricably linked to that of
group behavior, it is important to clarify the relation between these
concepts. By "social identity" we refer, in Tajfel's
own words, to



> 
> 
> that part of an individual's self-concept which derives from his
> knowledge of his membership of a social group (or groups) together
> with the value and emotional significance attached to that membership.
> (Tajfel 1981: 255)
> 
> 
> 



Note that a crucial feature of social identity is that one's
identification with the group is in some sense a conscious choice: one
may accidentally belong to a group, but we can meaningfully talk of
social identification only when being a group-member becomes (at least
in part) constitutive of who one is. According to Tajfel's
theory, when we categorize ourselves as belonging to a particular
group, the perception and definition of the self--as well as our
motives--change. That is, we start perceiving ourselves and our
fellow group-members along impersonal, "typical"
dimensions that characterize the group to which we belong. Such
dimensions include specific roles and the beliefs (or actions) that
accompany them.



Turner et al.'s (1987) "self-categorization theory"
provides a more specific characterization of self-perception, or
self-definition, as a system of cognitive self-schemata that filter
and process information. Such schemata result in a representation of
the social situation that guides the choice of appropriate action.
This system has at least two major components, i.e., social and
personal identity. Social identity refers to self-descriptions related
to group memberships. Personal identity refers to self-descriptions
such as individual character traits, abilities, and tastes. Although
personal and social identities are mutually exclusive levels of
self-definition, this distinction must be taken as an approximation
(in that there are many interconnections between social and personal
identities). It is, however, important to recognize that we often
perceive ourselves primarily in terms of our relevant group
memberships rather than as differentiated, unique individuals.
So--depending on the situation--personal or group identity
will become salient (Brewer 1991).



For example, when one makes interpersonal comparisons between oneself
and other group-members, personal identity will become salient;
instead, group identity will become salient in situations in which
one's group is compared to another group. Within a group, all
those factors that lead members to categorize themselves as different
(or endowed with special characteristics and traits) will enhance
personal identity. If a group has to solve a common task, but each
member is to be rewarded according to her contribution, personal
abilities are highlighted and individuals will perceive themselves as
unique and different from the rest of the group. Conversely, if all
group-members are to equally share the reward for a jointly performed
task, group identification will be enhanced. When the difference
between self and fellow group-members is accentuated, we are likely to
observe selfish motives and self-favoritism against other
group-members. When instead group identification is enhanced, in-group
favoritism against out-group members will be activated, as well as
behavior contrary to self-interest.



According to Turner, social identity is basically a cognitive
mechanism whose adaptive function is to make "group
behavior" possible. Whenever social identification becomes
salient, a cognitive mechanism of categorization is activated in such
a way to produce perceptual and behavioral changes. Such
categorization is called a stereotype, the prototypical description of
what members of a given category are (or are believed to be). It is a
cluster of physical, mental and psychological characteristics
attributed to a "typical" member of a given group.
Stereotyping, like any other categorization process, activates scripts
or schemata, and what we call group behavior is nothing but scripted
behavior. For example, the category "Asian student" is
associated with a cluster of behaviors, personality traits, and
values: we often think of Asian students as respectful, diligent,
disciplined, and especially good with technical subjects. When
thinking of an Asian student solely in terms of group membership, we
attribute her the stereotypical characteristics associated with her
group, so she becomes interchangeable with other group-members. When
we perceive people in terms of stereotypes, we depersonalize them and
see them as "typical" members of their group. The same
process is at work when we perceive ourselves as group-members:
self-stereotyping is a cognitive shift from "perceiving oneself
as unique" to "perceiving oneself in terms of the
attributes that characterize the group". It is this cognitive
shift that mediates group behavior.



Group behavior (as opposed to individual behavior) is characterized by
features such as a perceived similarity between group-members,
cohesiveness, a tendency to cooperate to achieve common goals, shared
attitudes or beliefs, and conformity to group norms. Once an
individual self-categorizes as member of a group, she will perceive
herself as "depersonalized" and similar to other
group-members in the relevant stereotypical dimensions. Insofar as
group-members perceive their interests and goals as
identical--because such interests and goals are stereotypical
attributes of the group--self-stereotyping will induce a
group-member to embrace such interests and goals as her own. It is
thus predicted that pro-social behavior will be enhanced by group
membership, and diluted when people act in an individualistic mode
(Brewer 1979).



The groups with which we happen to identify ourselves may be very
large (as in the case in which one self-defines as Muslim or French),
or as small as a friends' group. Some general group identities
may not involve specific norms, but there are many cases in which
group identification and social norms are inextricably connected. In
that case group-members believe that certain patterns of behavior are
unique to them, and use their distinctive norms to *define*
group membership. Many close-knit groups (such as the Amish or the
Hasidic Jews) enforce norms of separation proscribing marriage with
outsiders, as well as specific dress codes and a host of other
prescriptive and proscriptive norms. There, once an individual
perceives herself as a group-member, she will adhere to the group
prototype and behave in accordance with it. Hogg and Turner (1987)
have called the process through which individuals come to conform to
group norms "referent informational influence".



Group-specific norms have (among other things) the twofold function of
minimizing perceived differences among group-members and maximizing
differences between the group and outsiders. Once formed, such norms
become stable cognitive representations of appropriate behavior as a
group-member. Social identity is built around group characteristics
and behavioral standards, and hence any perceived lack of conformity
to group norms is seen as a threat to the legitimacy of the group.
Self-categorization accentuates the similarities between one's
behavior and that prescribed by the group norm, thus causing
conformity as well as the disposition to control and punish
transgressors. In the social identity framework, group norms are
obeyed because one identifies with the group, and conformity is
mediated by self-categorization as an in-group member. A telling
historical example of the relationship between norms and group
membership was the division of England into the two parties of the
Roundheads and Cavaliers. Charles Mackay reports that



> 
> 
> in those days every species of vice and iniquity was thought by the
> Puritans to lurk in the long curly tresses of the monarchists, while
> the latter imagined that their opponents were as destitute of wit, of
> wisdom, and of virtue, as they were of hair. A man's locks were
> a symbol of his creed, both in politics and religion. The more
> abundant the hair, the more scant the faith; and the balder the head,
> the more sincere the piety. (Mackay 1841: 351)
> 
> 
> 



It should be noted that in this framework social norms are defined by
collective--as opposed to personal--beliefs about
appropriate behaviors (Homans 1950, 1961). To a certain extent, this
characterization of social norms is closer to recent accounts than it
is to Parsons' socialized actor theory. On the other hand, a
distinct feature of the social identity framework is that
people's motivation to conform comes from their desire to
validate their identity as group-members. In short, there are several
empirical predictions one can draw from such a framework. Given the
theory's emphasis on identity as a motivating factor, conformity
to a norm is not assumed to depend on an individual's
internalization of that norm; in fact, a change in social status or
group membership will bring about a change in the norms relevant to
the new status/group. Thus a new norm can be quickly adopted without
much interaction, and beliefs about identity validation may change
very rapidly under the pressure of external circumstances. In this
case, not just norm compliance, but norms themselves are potentially
unstable.



The experimental literature on social dilemmas has utilized the
"priming of group identity" as a mechanism for promoting
cooperative behavior (Dawes 1980; Brewer & Schneider 1990). The
typical hypothesis is that a pre-play, face-to-face communication
stage may induce identification with the group, and thus promote
cooperative behavior among group-members. In effect, rates of
cooperation have been shown to be generally higher in social dilemma
experiments preceded by a pre-play communication stage (Dawes 1991).
However, it has been argued that face-to-face communication may
actually help group-members gather relevant information about one
another: such information may therefore induce subjects to trust each
other's promises and act cooperatively, regardless of any group
identification. In this respect, it has been shown that communication
per se does not foster cooperation, unless subjects are allowed to
talk about relevant topics (Bicchieri & Lev-On 2007). This
provides support for the view that communication does not enhance
cohesion but rather focuses subjects on relevant rules of behavior,
which do not necessarily depend on group identification.



Cooperative outcomes can thus be explained without resorting to the
concept of social identity. A social identity explanation appears to
be more appropriate in the context of a relatively stable environment,
where individuals have had time to make emotional investments (or at
least can expect repeated future interactions within the same group).
In artificial lab settings, where there are no expectations of future
interactions, the concept of social identity seems less persuasive as
an explanation of the observed rates of cooperation. On the other
hand, we note that social identity does appear to play a role in
experimental settings in which participants are divided into separate
groups. (In that case, it has been shown that participants categorize
the situation as "we versus them", activating in-group
loyalty and trust, and an equal degree of mistrust toward the
out-group; Kramer & Brewer 1984; Bornstein & Ben-Yossef
1994.)



Even with stable environments and repeated interactions, however, a
theory of norm compliance in terms of social identity cannot avoid the
difficulty of making predictions when one is simultaneously committed
to different identities. We may concurrently be workers, parents,
spouses, friends, club members, and party affiliates, to name but a
few of the possible identities we embrace. For each of them there are
rules that define what is appropriate, acceptable, or good behavior.
In the social identity framework, however, it is not clear what
happens when one is committed to different identities that may involve
conflicting behaviors.



Finally, there is ample evidence that people's perceptions may
change very rapidly. Since in this framework norms are defined as
shared perceptions about group beliefs, one would expect
that--whenever all members of a group happen to believe that
others have changed their beliefs about core membership
rules--the very norms that define membership will change. The
study of fashion, fads and speculative bubbles clearly shows that
there are some domains in which rapid (and possibly disruptive)
changes of collective expectations may occur; it is, however, much
less clear what sort of norms are more likely to be subject to rapid
changes (think of dress codes rather than codes of honor). The social
identity view does not offer a theoretical framework for
differentiating these cases: although some norms are indeed related to
group membership, and thus compliance may be explained through
identity-validation mechanisms, there appear to be limits to the
social identity explanation.


## 4. Early Theories: Cost-Benefit Models



Early rational choice models of conformity maintained that, since
norms are upheld by sanctions, compliance is merely a
payoff-maximizing strategy (Rommetveit 1955; Thibaut & Kelley
1959): when others' approval and disapproval act as external
sanctions, we have a "cost-benefit model" of compliance
(Axelrod 1986; James Coleman 1990). Rule-complying strategies are
rationally chosen in order to avoid negative sanctions or to attract
positive sanctions. This class of rational choice models defines norms
behaviorally, equating them with patterns of behavior (while
disregarding expectations or values). Such approach relies heavily on
sanctions as a motivating factor. According to Axelrod (1986), for
example, if we observe individuals to follow a regular pattern of
behavior and to be punished if they act otherwise, then we have a
norm. Similarly, Coleman (1990) argues that a norm coincides with a
set of sanctions that act to direct a given behavior.



However, it has been shown that not all social norms involve sanctions
(Diamond 1935; Hoebel 1954). Moreover, sanctioning works generally
well in small groups and in the context of repeated interactions,
where the identity of participants is known and monitoring is
relatively easy. Still, even in such cases there may be a so-called
*second-order* public goods problem. That is, imposing negative
sanctions on transgressors is in everybody's interest, but the
individual who observes a transgression faces a dilemma: she is to
decide whether or not to punish the transgressor, where punishing
typically involves costs; besides, there is no guarantee that other
individuals will also impose a penalty on transgressors when faced
with the same dilemma. An answer to this problem has been to assume
that there exist "meta-norms" that tell people to punish
transgressors of lower-level norms (Axelrod 1986). This solution,
however, only shifts the problem one level up: upholding the meta-norm
itself requires the existence of a higher-level sanctioning
system.



Another problem with sanctions is the following: a sanction, to be
effective, must be recognized as such. Coleman and Axelrod typically
take the repeated prisoner's dilemma game as an example of the
working of sanctions. However, in a repeated prisoner's dilemma
the same action ("C" or "D") must serve as
both the sanctioning action and the target action. By simply looking
at behavior, it is unclear whether the action is a function of a
sanction or a sanction itself. It thus becomes difficult to determine
the presence of a norm, or to assess its effect on choice as distinct
from the individual strategies of players.



A further consideration weakens the credibility of the view that norms
are upheld only because of external sanctions. Often we keep
conforming to a norm even in situations of complete anonymity, where
the probability of being caught transgressing is almost zero. In this
case fear of sanctions cannot be a motivating force. As a consequence,
it is often argued that cases of "spontaneous" compliance
are the result of internalization (Scott 1971): people who have
developed an internal sanctioning system feel guilt and shame at
behaving in a deviant way. Yet, we have seen that the Parsonian view
of internalization and socialization is inadequate, as it leads to
predictions about compliance that often run counter to empirical
evidence.



In particular, James Coleman (1990) has argued in favor of reducing
internalization to rational choice, insofar as it is in the interest
of a group to get another group to internalize certain norms. In this
case internalization would still be the result of some form of
socialization. This theory faces some of the same objections raised
against Parsons' theory: norms that are passed on from parents
to children, for example, should be extremely resistant to change;
hence, one should expect a high degree of correlation between such
norms and behavior, especially in those cases where norms prescribe
specific kinds of actions. However, studies of normative beliefs about
honesty--which one typically acquires during childhood--show
that such beliefs are often uncorrelated with behavior (Freeman &
Ataov 1960).



Bicchieri (1990, 1997) has presented a third, alternative view about
internalization. This view of internalization is cognitive, and is
grounded on the assumption that social norms develop in small,
close-knit groups where ongoing interactions are the rule. Once an
individual has learned to behave in a way consistent with the
group's interests, she will tend to persist in the learned
behavior unless it becomes clear that--on average--the cost
of upholding the norm significantly outweighs the benefits. Small
groups can typically monitor their members' behavior and
successfully employ retaliation whenever free-riding is observed. In
such groups an individual will learn, maybe at some personal cost, to
cooperate; she will then uphold the cooperative norm as a
"default rule" in any new encounter, unless it becomes
evident that the cost of conformity has become excessive. The idea
that norms may be "sluggish" is in line with well-known
results from cognitive psychology showing that, once a norm has
emerged in a group, it will tend to guide the behavior of its members
even when they face a new situation (or are isolated from the original
group; Sherif 1936).



Empirical evidence shows that norm-abiding behavior is not, as the
early rational choice models would have it, a matter of cost/benefit
calculation. Upholding a norm that has led one to fare reasonably well
in the past is a way of economizing on the effort one would have to
exert to devise a strategy *when facing a new situation*. This
kind of "bounded rationality" approach explains why people
tend to obey norms that sometimes put them at a disadvantage, as is
the case with norms of honesty. This does not mean, however, that
external sanctions never play a role in compliance: for example, in
the initial development of a norm sanctions may indeed play an
important role. Yet, once a norm is established, there are several
mechanisms that may account for conformity.



Finally, the view that one conforms *only* because of the
threat of negative sanctions does not distinguish norm-abiding
behavior from an obsession or an entrenched habit; nor does that view
distinguish social norms from hypothetical imperatives enforced by
sanctions (such as the rule that prohibits naked sunbathing on public
beaches). In these cases avoidance of the sanctions associated with
transgressions constitutes a decisive reason to conform, independently
of what others do. In fact, in the traditional rational choice
perspective, the only expectations that matter are those about the
sanctions that follow compliance or non-compliance. In those
frameworks, beliefs about how other people will act--as opposed
to what they expect us to do--are not a relevant explanatory
variable: however, this leads to predictions about norm compliance
that often run counter to empirical evidence.


## 5. Game-Theoretic Accounts



The traditional rational choice model of compliance depicts the
individual as facing a decision problem in isolation: if there are
sanctions for non-compliance, the individual will calculate the
benefit of transgression against the cost of norm compliance, and
eventually choose so as to maximize her expected utility. Individuals,
however, seldom choose in isolation: they know the outcome of their
choice will depend on the actions and beliefs of other individuals.
Game theory provides a formal framework for modeling strategic
interactions.



Thomas Schelling (1960), David Lewis (1969), Edna Ullmann-Margalit
(1977), Robert Sugden (1986) and, more recently, Peyton Young (1993),
Cristina Bicchieri (1993), and Peter Vanderschraaf (1995) have
proposed a game-theoretic account according to which a norm is broadly
defined as an *equilibrium* of a strategic interaction. In
particular, a Nash equilibrium is a combination of strategies (one for
each individual), such that each individual's strategy is a best
reply to the others' strategies. Since it is an equilibrium, a
norm is supported by self-fulfilling expectations in the sense that
players' beliefs are consistent, and thus the actions that
follow from players' beliefs will validate those very beliefs.
Characterizing social norms as equilibria has the advantage of
emphasizing the role that expectations play in upholding norms. On the
other hand, this interpretation of social norms does not *prima
facie* explain why people prefer to conform if they expect others
to conform.



Take for example *conventions* such as putting the fork to the
left of the plate, adopting a dress code, or using a particular sign
language. In all these cases, my choice to follow a certain rule is
conditional upon expecting most other people to follow it. Once my
expectation is met, I have every reason to adopt the rule in question.
In fact, if I do not use the sign language everybody else uses, I will
not be able to communicate. It is in my immediate interest to follow
the convention, since my main goal is to coordinate with other people.
In the case of conventions, there is a continuity between the
individual's self-interest and the interests of the community
that supports the convention. This is the reason why David Lewis
models conventions as equilibria of *coordination games*. Such
games have multiple equilibria, but once one of them has been
established, players will have every incentive to keep playing it (as
any deviation will be costly).



Take instead a norm of cooperation. In this case, the expectation that
almost everyone abides by it may not be sufficient to induce
compliance. If everyone is expected to cooperate one may be tempted,
if unmonitored, to behave in the opposite way. The point is that
conforming to *social norms*, as opposed to conventions, is
almost never in the immediate interest of the individual. Often there
is a discontinuity between the individual's self-interest and
the interests of the community that supports the social norm.



The typical game in which following a norm would provide a better
solution (than the one attained by self-centered agents) is a
*mixed-motive game* such as the prisoner's dilemma or the
trust game. In such games the unique Nash equilibrium represents a
suboptimal outcome. It should be stressed that--whereas a
convention is one among several equilibria of a coordination
game--a social norm can never be an equilibrium of a mixed-motive
game. However, Bicchieri (2006) has argued that when a norm exists it
*transforms* the original mixed-motive game into a coordination
one. As an example, consider the following prisoner's dilemma
game
 (Figure 1),
 where the payoffs are B=Best, S=Second, T=Third, and W=Worst. Clearly
the only Nash equilibrium is to defect (D), in which case both players
get (T,T), a suboptimal outcome. Suppose, however, that society has
developed a norm of cooperation; that is, whenever a social dilemma
occurs, it is commonly understood that the parties should privilege a
cooperative attitude. Should, however, does not imply
"will", therefore the new game generated by the existence
of the cooperative norm has two equilibria: either both players defect
or both cooperate.



![Two tables with a large arrow going from the left table to the right table. Both tables are 4x4 with the rows labeled 'Self' and top row 'C' and bottom row 'D' and the columns labeled 'Other' and the left column 'C' and the right column 'D'. The left table has the caption 'PD Game' and the cells are left to right and top to bottom 'S,S', 'W,B', 'B,W', ''T,T'. The right table has the caption 'Coordination Game' and the cells are 'B,B', 'W,T', 'T,W', 'S,S'. ](fig1.svg)

Figure 1




Note that, in the new coordination game (which was created by the
existence of the cooperative norm), the payoffs are quite different
from those of the original prisoner's dilemma. Thus there are
two equilibria: if both players follow the cooperative norm they will
play an optimal equilibrium and get (B,B), whereas if they both choose
to defect they will get the suboptimal outcome (S,S). Players'
payoffs in the new coordination game differ from the original payoffs
because their preferences and beliefs will reflect the existence of
the norm. More specifically, if a player knows that a cooperative norm
exists and has the right kind of expectations, then she will have a
preference to conform to the norm in a situation in which she can
choose to cooperate or to defect. In the new game generated by the
norm's existence, choosing to defect when others cooperate is
not a good choice anymore (T,W). To understand why, let us look more
closely to the preferences and expectations that underlie the
conditional choice to conform to a social norm.



Bicchieri (2006) defines the expectations that underlie norm
compliance, as follows:



(a)
*Empirical expectations:* individuals believe that a
sufficiently large subset of the relevant group/population conforms to
the norm in situations of type *S* and either
(b)
*Normative expectations:* individuals believe that a
sufficiently large subset of the relevant group/population expects
them to conform to the norm in situations of
type *S*;


or



(b')
*Normative expectations with sanctions*: individuals
believe that a sufficiently large subset of the relevant
group/population expects them to conform to the norm in situations of
type *S*, prefers them to conform and may sanction
behavior.


Note that universal compliance is not usually needed for a norm to
exist. However, how much deviance is socially tolerable will depend on
the norm in question. Group norms and well-entrenched social norms
will typically be followed by almost all members of a group or
population, whereas greater deviance is usually accepted when norms
are new or they are not deemed to be socially important. Furthermore,
as it is usually unclear how many people follow a norm, different
individuals may have different beliefs about the size of the group of
followers, and may also have different thresholds for what
"sufficiently large" means. What matters to conformity is
that an individual believes that her threshold has been reached or
surpassed. For a critical assessment of the above definition of
norm-driven preferences, see Hausman (2008).



Brennan et al. (2013) also argue that norms of all kinds share in an
essential structure. Norms are clusters of normative attitudes in a
group, combined with the knowledge that such a cluster of attitudes
exists. On their account, "A normative principle *P* is a
norm within a group *G* if and only if:


1. A significant proportion of the members of *G*
have *P*-corresponding normative attitudes; and
2. A significant proportion of the members of *G*
know that a significant proportion of the members of *G* have
*P*-corresponding attitudes" (Brennan et al. 2013:
29)



On this account, a "*P*-corresponding normative
attitude" is understood to be a judgment, emotional state,
expectation, or other properly first personal normative belief that
supports the principle *P* (e.g., Alice thinking most people
*should* *P* would count as a normative attitude).
 Condition (i)
 is meant to reflect genuine first personal normative commitments,
attitudes or beliefs.
 Condition (ii)
 is meant to capture those cases where individuals know that a large
part of their group also shares in those attitudes. Putting conditions
(i) and (ii) together offers a picture that the authors argue allows
for explanatory work to be done on a social-level normative concept
while remaining grounded in individual-level attitudes.



Consider again the new coordination game of
 Figure 1:
 for players to obey the norm, and thus choose C, it must be the case
that each expects the other to follow it. In the original
prisoner's dilemma, empirical beliefs would not be sufficient to
induce cooperative behavior. When a norm exists, however, players also
believe that others believe they should obey the norm, and may even
punish them if they do not. The combined force of empirical and
normative expectations makes norm conformity a compelling choice, be
it because punishment may follow or just because one recognizes the
legitimacy of others' expectations (Sugden 2000).



It is important to understand that conformity to a social norm is
always conditional on the expectations of what the relevant other/s
will do. We *prefer* to comply with the norm as we have certain
expectations. To make this point clear, think of the player who is
facing a typical one-shot prisoner's dilemma with an unknown
opponent. Suppose the player knows a norm of cooperation exists and is
generally followed, but she is uncertain as to whether the opponent is
a norm-follower. In this case the player is facing the following
situation
 (Figure 2).



![See Figure 1 for description of the PD Game and Coordination Game tables. This diagram has a top node 'Nature' with arrows pointing to the PD Game table on the left and the Coordination Game table on the right. The left arrow is labeled 'Type 1' and (1-p) and the right arrow 'Type 2' and (p).](fig2.svg)

Figure 2




With probability *p*, the opponent is a norm-following type,
and with probability \(1 - p\) she is not. According to Bicchieri,
conditional preferences imply that having a reason to be fair,
reciprocate or cooperate *in a given situation* does not entail
having any general motive or disposition to be fair, reciprocate or
cooperate as such. Having conditional preferences means that one may
follow a norm in the presence of the relevant expectations, but
disregard it in its absence. Whether a norm is followed at a given
time depends on the actual proportion of followers, on the
expectations of conditional followers about such proportion, and on
the combination of individual thresholds.



As an example, consider a community that abides by strict norms of
honesty. A person who, upon entering the community, systematically
violates these norms will certainly be met with hostility, if not
utterly excluded from the group. But suppose that a large group of
thieves makes its way into this community. In due time, people would
cease to expect honesty on the part of others, and would find no
reason to be honest themselves in a world overtaken by crime. In this
case, probably norms of honesty would cease to exist, as the strength
of a norm lies in its being followed by many of the members of the
relevant group (which in turn reinforces people's expectations
of conformity).



What we have discussed is a "rational reconstruction" of
what a social norm is. Such a reconstruction is meant to capture some
essential features of norm-driven behavior; also, this analysis helps
us distinguish social norms from other constructs such as conventions
or personal norms. A limit of this account, however, is that it does
not indicate how such equilibria are attained or, in other terms, how
expectations become self-fulfilling.



While neoclassical economics and game theory traditionally conceived
of institutions as exogenous constraints, research in political
economy has generated new insights into the study of *endogenous
institutions*. Specifically, endogenous norms have been shown to
restrict the individual's action set and drive preferences over
action profiles (Bowles 1998; Ostrom 2000). As a result, the
"standard" economic framework positing exogenous (and in
particular self-centered) preferences has come under scrutiny. Widely
documented deviations from the predictions of models with
self-centered agents have informed alternative accounts of individual
choice (for one of the first models of "interdependent
preferences", see Stigler & Becker 1977).



Some alternative accounts have helped reconcile insights about
norm-driven behavior with instrumental rationality (Elster 1989b).
Moreover, they have contributed to informing the design of laboratory
experiments on non-standard preferences (for a survey of early
experiments, see Ledyard 1995; more recent experiments are reviewed by
Fehr & Schmidt 2006 and Kagel & Roth 2016). In turn,
experimental findings have inspired the formulation of a wide range of
models aiming to rationalize the behavior observed in the lab (Camerer
2003; Dhami 2016).



It has been argued that the upholding of social norms could simply be
modeled as the optimization of a utility function that includes the
others' welfare as an argument. For instance, consider some of
the early "social preference" theories, such as Bolton and
Ockenfels' (2000) or Fehr and Schmidt's (1999) models of
inequity aversion. These frameworks can explain a good wealth of
evidence on preferences for equitable income distributions; they
cannot however account for *conditional preferences* like those
reflecting principles of reciprocity (e.g., I will keep the common
bathroom clean, if I believe my roommates do the same). As noted
above, the approach to social norms taken by philosophically-inclined
scholars has emphasized the importance of conditional preferences in
supporting social norms. In this connection, we note that some of the
social preference theories do account for motivations conditional on
*empirical* beliefs, whereby a player upholds a principle of
"fair" behavior if she believes her co-players will uphold
it too (Rabin 1993; Dufwenberg & Kirchsteiger 2004; Falk &
Fischbacher 2006; Charness & Rabin 2002). These theories
presuppose that players are hardwired with a notion of fair or kind
behavior, as exogenously defined by the theorist. Since they
implicitly assume that all players have internalized a
unique--exogenous--normative standpoint (as reflected in
some notion of fairness or kindness), these theories do not explicitly
model *normative* expectations. Hence, players'
preferences are assumed to be conditional solely on their empirical
beliefs; that is, preferences are conditional on whether others will
behave fairly (according to an exogenous principle) or not.



That said, we stress that social preferences should not be conflated
with social norms. Social preferences capture *stable
dispositions* toward an exogenously defined principle of conduct
(Binmore 2010). By contrast, social norms are better studied as
*group-specific solutions* to strategic problems (Sugden 1986;
Bicchieri 1993; Young 1998b). Such solutions are brought about by a
particular class of preferences ("norm-driven
preferences"), conditional on the relevant set of empirical
beliefs and normative expectations. In fact, we stress that
"what constitutes fair or appropriate behavior" often
varies with cultural or situational factors (Henrich et al. 2001;
Cappelen et al. 2007; Ellingsen et al. 2012). Accounting for
endogenous expectations is therefore key to a full understanding of
social norms.



Relatedly, Guala (2016) offers a game-theoretic account of
institutions, arguing that institutions are sets of rules in
equilibrium. Guala's view incorporates insights from two
competing accounts of institutions: institutions-as-rules (perhaps
best rendered by North 1990), and institutions-as-equilibria. From the
first account, he captures the idea that institutions create rules
that help to guide our behaviors and reduce uncertainty. With rules in
place, we more or less know what to do, even in new situations. From
the second, he captures the idea that institutions are solutions to
coordination problems that arise from our normal interactions. The
institutions give us reasons to follow them. The function of the
rules, then, is to point to actions that promote coordination and
cooperation. Because of the equilibrium nature of the rules, each
individual has an incentive to choose those actions, provided others
do too. Guala relies on a correlated equilibrium concept to unite the
rules and equilibria accounts. On this picture, an institution is
simply a correlated equilibrium in a game, where other correlated
equilibria would have been possible.



Thrasher (2018) offers a comparative-functional analysis of norms that
broadly aligns with the Bicchieri (2006) framework to help understand
the durability of "bad norms." Abbink et al. (2017) use
public goods-like experiments to show how peer punishment can hold
inefficient norms in place. This general framework can be helpful to
understand why duels and honor killings can become stable (e.g.
Thrasher and Handfield 2018, Handfield and Thrasher 2019). This work
explores the signaling function of socially costly norms.



An alternative class of models explains norm compliance in terms of
social image or self-image concerns (e.g., Andreoni and Bernheim 2009;
Benabou and Tirole 2006, 2011). These models assume that one
tries to signal (to others or to one's future self) that one has
good "personal traits", with such type-specific traits
being imperfectly observed. More precisely, Benabou and Tirole
(2006) model the individual's utility from contributing to a
public good as a function of (i) material payoffs, (ii) intrinsic
rewards from behaving altruistically, and (iii) reputational returns;
in particular, the authors assume that reputational returns depend on
the observers' posterior expectations of the individual's
type. Benabou and Tirole then consider (a refinement of)
signaling equilibria, thereby allowing for multiple solutions to occur
as a result of the interplay of individual motivations and of the
level of observability of the actions. While models with reputational
concerns do not explicitly define normative expectations, they
generally posit that players care about their reputation under the
assumption that acting altruistically is good or appropriate. Looking
ahead, there is still work to do to fully formalize the interplay of
(endogenous) normative expectations and empirical beliefs within a
general model that is applicable to *any* game setting. Such a
model should probably build on the "psychological game
theory" framework (for discussion, see Battigalli and Dufwenberg
2022, p. 857; see also Bicchieri and Sontuoso 2015).


## 6. Experimental Evidence



In what follows we focus on lab experiments that identify social norms
by explicitly measuring both empirical and normative expectations.



Xiao and Bicchieri (2010) designed an experiment to investigate the
impact on trust games of two potentially applicable--but
conflicting--principles of conduct, namely, *equality* and
*reciprocity*. Note that the former can be broadly defined as a
rule that recommends minimizing payoff differences, whereas the latter
recommends taking a similar action as others (regardless of payoff
considerations). The experimental design involved two trust game
variants: in the first one, players started with equal endowments; in
the second one, the investor was endowed with twice the money that the
trustee was given. In both cases, the investor could choose to
transfer a preset amount of money to the trustee or keep it all. Upon
receiving the money, the trustee could in turn keep it or else
transfer back some of it to the investor: in the equal endowment
condition ("baseline treatment"), both equality and
reciprocity dictate that the trustee transfer some money back to the
investor; by contrast, in the unequal endowment condition
("asymmetry treatment"), equality and reciprocity dictate
different actions as the trustee could guarantee payoff equality only
by making a zero back-transfer. Xiao and Bicchieri elicited
subjects' first- and second-order *empirical beliefs*
("how much do you think other participants in your role will
transfer to their counterpart?"; "what does your
counterpart think you will do?") and *normative
expectations* ("how much do you think your counterpart
believes you should transfer to her?"). The experimental results
show that a majority of trustees returned a positive amount whenever
reciprocity would reduce payoff inequality (in the baseline
treatment); by contrast, a majority of trustees did not reciprocate
the investors' transfer when doing so would increase payoff
inequality (in the asymmetry treatment). Moreover, investors correctly
believed that less money would be returned in the asymmetry treatment
than in the baseline treatment, and most trustees correctly estimated
investors' beliefs in both treatments. However, in the asymmetry
treatment empirical beliefs and normative expectations conflicted:
this highlights that, when there is ambiguity as to which principle of
conduct is in place, each subject will support the rule of behavior
that favors her most.



Reuben and Riedl (2013) examine the enforcement of norms of
contribution to public goods in homogeneous and heterogeneous groups,
such as groups whose members vary in their endowment, contribution
capacity, or marginal benefits. In particular, Reuben and Riedl are
interested in the normative appeal of two potentially applicable
rules: the *efficiency rule* (prescribing maximal contributions
by all) and the class of *relative contribution rules*
(prescribing a contribution that is "fair" relative to the
contributions of others; e.g., equality and equity rules). Reuben and
Riedl's results show that, in the absence of punishment, no
positive contribution norm emerged and all groups converged toward
free-riding. By contrast, with punishment, contributions were
consistent with the prescriptions of the efficiency rule in a
significant subset of groups (irrespective of the type of group
heterogeneity); in other groups, contributions were consistent with
relative contribution rules. These results suggest that even in
heterogeneous groups individuals can successfully enforce a
contribution norm. Most notably, survey data involving third parties
confirmed well-defined yet conflicting normative views about the
aforementioned contribution rules; in other words, both efficiency and
relative contribution rules are normatively appealing, and are indeed
potential candidates for emerging contribution norms in different
groups.



Bicchieri and Chavez (2010) designed an experiment to investigate norm
compliance in ultimatum games. Specifically, their experiment involved
a variant of the ultimatum game whereby the proposer could choose one
of the following three options: *($5, $5)*, *($8, $2)*,
or *Coin* (in which case one of the other two allocations would
be selected at random). This design allows for two plausible notions
of fairness: as an *equal outcome* ($5, $5) or as a *fair
procedure* (Coin). The experimenters elicited subjects'
normative expectations about the actions they thought would be
considered fair by most participants: proposers and responders showed
a remarkable degree of agreement in their notions of fairness, as most
subjects believed that a majority of participants deemed both ($5, $5)
and Coin to be appropriate. Further, the experimenters had subjects
play three instances of the above ultimatum game under different
information conditions. In the "full information"
condition, all participants knew that the Coin option was available,
and that responders would know if their respective proposer had chosen
Coin. In the "private information" condition, responders
did not know that Coin was available to proposers, and proposers were
aware of responders' ignorance. In the "limited
information" condition, participants knew that the Coin option
was available, but responders would not be able to distinguish whether
their respective proposer had implemented one of the two allocations
directly or had chosen Coin instead. The experimental results show
that when normative expectations supporting the Coin option were
either absent (in the *private* condition) or could be defied
without consequence (in the *limited* condition), the frequency
of choice of ($5, $5) and ($8, $2), respectively, were considerably
higher than those of Coin. Moreover, the frequency of Coin choices was
highest in the *public* information condition, where such
option was common knowledge and its outcome transparent: this shows
that there proposers followed the rule of behavior that favored them
most, and that such a rule was effectively a social norm. On the other
hand, substantial norm evasion characterized proposers' behavior
in the limited information condition, where ($8, $2) was the most
frequent choice.



In a subsequent study, Chavez and Bicchieri (2013) measured empirical
and normative expectations (as well as behavior) of third parties who
were given the opportunity to add to or deduct from the payoffs of
subjects who had participated in an ultimatum game. Third parties
tended to reward subjects involved in equal allocations and to
compensate victims of unfair allocations (rather than punish unfair
behavior); on the other hand, third parties were willing to punish
when compensation was not an available option. The experimental
results further show that third parties shared a notion of fairness
(as indicated by their normative expectations), and that such notion
was sensitive to contextual differences.



Krupka and Weber (2013) introduced an interesting procedure for
identifying social norms by means of pre-play coordination games. In
brief, using alternative (between-subjects) variants of the dictator
game, Krupka and Weber had participants assess the extent to which
different actions were collectively perceived as socially appropriate:
subjects providing these ratings effectively faced a coordination
game, as they were incentivized to match the modal response given by
others in the same situation (such a pre-play coordination game was
intended to verify the presence of shared normative expectations).
Krupka and Weber went on to use these elicited assessments to predict
other subjects' compliance with the relevant social norm in each
dictator game variant (for another application of the same elicitation
procedure, see Gachter et al. 2013).



Similarly, Schram and Charness' (2015) proposed a procedure for
inducing a shared understanding of the relevant rule of behavior, in
the lab. In short, Schram and Charness had participants in dictator
games receive advice from a group of third parties. The information
received simply revealed what a group of uninvolved subjects thought
dictators *ought to do*: as such, the information received
generated an exogenous variation in the dictators' normative
expectations. Schram and Charness' results show that choices are
indeed affected by this information.



Bicchieri and Xiao (2009) designed an experiment to investigate what
happens when empirical and normative expectations conflict. To that
end, participants in a dictator game were exposed to different pieces
of information. Specifically, two groups of dictators were given some
"descriptive information"; that is, they were told what
other subjects had *done* in another session (i.e., one group
was told that previous participants had made for the most part a
generous offer, while the other group was told that most participants
had made a selfish offer). Further, another two groups of dictators
were given some "normative information"; that is, they
were told what previous subjects said *ought to be done* (i.e.,
one group was told that most previous participants thought that one
should make a generous offer, while the other group was told that most
participants thought that one should make a selfish offer). Other
groups were given both descriptive and normative information. The
experimental results show that--whenever such information did not
conflict--both descriptive and normative messages had a
significant influence on dictators' own expectations and
subsequent choices. When messages conflicted in that one indicated
generosity and the other indicated selfishness, only the descriptive
information affected dictators' behavior. This suggests that if
people recognize that others are breaching the norm, then they will no
longer feel compelled to follow the relevant rule of behavior
themselves.



To conclude, the studies surveyed here provide evidence of the role
played by expectations in affecting behavior in a variety of social
dilemmas. In this regard, we note that in contrast to the vast
literature on empirical beliefs, the number of lab studies that
directly measure normative expectations is relatively limited: more
research is clearly needed to investigate the interplay of empirical
and normative information about applicable rules of behavior.


## 7. Evolutionary Models



Thus far we have examined accounts of social norms that take for
granted that a particular norm exists in a population. However, for a
full account of social norms, we must answer two questions related to
the dynamics of norms. First, we must ask how a norm can emerge. Norms
require a set of corresponding beliefs and expectations to support
them, and so there must be an account of how these arise. Second, we
must investigate the conditions under which a norm is stable under
some competitive pressure from other norms. Sometimes, multiple
candidate norms vie for dominance in a population. Even if one norm
has come to dominate the population, new norms can try to
"invade" the existing norm's population of
adherents.



Let us now turn to the question of norm emergence. Here we can see
three classes of models: first, a purely biological approach, second,
a more cognitive approach, and third, a structured interactions
approach. The most famous of the biological approaches to norms seek
to explain cooperative behavior. The simplest models are kin selection
models (Hamilton 1964). These models seek to explain altruistic
tendencies in animals by claiming that, as selection acts on genes,
those genes have an incentive to promote the reproductive success of
other identical sets of genes found in other animals. This mode of
explanation can provide an account of why we see cooperative behaviors
within families, but being gene-centered, cannot explain cooperative
behavior toward strangers (as strangers should not be sufficiently
genetically related to merit altruistic behavior).



Models of "reciprocal altruism" (Trivers 1971, 1985), on
the other hand, tell us that cooperative behavior has no chance of
evolving in random pairings, but will evolve in a social framework in
which individuals can benefit from building reputations for being nice
guys. Reciprocal altruism, however, does not require an evolutionary
argument; a simple model of learning in ongoing close-knit groups will
do, and has the further advantage of explaining why certain types of
cooperative behavior are more likely to emerge than others. All that
matters in these models is that agents can properly identify other
agents, such that they can maintain a record of their past behavior.
This allows for the possibility of reputations: people who have the
reputation of being cooperative will be treated cooperatively, and
those who have a reputation of being unfair will be treated
unfairly.



A variation on the idea of reciprocal altruism can be seen in Axelrod
(1986). Axelrod presents a "norms game" in which agents
probabilistically choose to comply with the norm, or deviate from it,
and then other agents can probabilistically choose to punish any
deviations at some cost to them. Agents can choose over time to be
more or less "bold", which determines the rate at which
they attempt defections, and they can likewise choose to be more or
less "vengeful", which determines how often they punish.
Axelrod noted that if the game is left like this, we find that the
stable state is constant defection and no punishment. However, if we
introduce a meta-norm--one that punishes people who fail to
punish defectors--then we arrive at a stable norm in which there
is no boldness, but very high levels of vengefulness. It is under
these conditions that we find a norm emerge and remain stable.
Axelrod's model aims to illustrate that norms require
meta-norms. That is, failure to retaliate against a defection must be
seen as equivalent to a defection itself. What Axelrod does not
analyze is whether there is some cost to being vigilant. Namely,
watching both defectors and non-punishers may have a cost that, though
nominal, might encourage some to abandon vigilance once there has been
no punishment for some time.



Bicchieri, Duffy and Tolle (2004) present an alternative model of norm
emergence to explain how a norm of impersonal trust/reciprocity can
emerge and survive in a heterogeneous population. This model does not
rely on a meta-norm of punishment; instead, it is purely driven by
repeated interactions of conditional strategies. In their model,
agents play anywhere from 1 to 30 rounds of a trust game for 1,000
iterations, relying on the 4 unconditional strategies, and the 16
conditional strategies that are standard for the trust game. After
each round, agents update their strategies based on the replicator
dynamic. As the number of rounds grows, a norm of impersonal
trust/reciprocity emerges in the population. Most interestingly,
however, the norm is not associated with a single strategy, but it is
supported by several strategies behaving in similar ways. This model
suggests that Trivers' basic model works well in normal social
contexts, but we can further enrich the story by allowing a social
norm to supervene on several behavioral strategies.



Muldoon et al. (2012) explore a simpler approach to norm emergence that
relies on individual reasoners weighing their individual interests
against their social sensitivity. This is done across a number of
model variants based on a simple standing ovation. A striking finding
of their "symmetric" model is that norm emergence is
fairly rare, but can also be distinguished from merely common
behaviors. A more cognitively demanding approach was taken by Muldoon,
Lisciandra and Hartmann (2012), in which bayesian reasoners can learn
to "discover" norms that were not present, and have no
particular value. This can happen when agents think there might be a
social rule, and then over-interpret social evidence. These models
combine to suggest that we should expect many arbitrary norms, rather
than a functionalist argument for the presence of norms.



The third prominent model of norm emergence comes from Brian Skyrms
(1996, 2004) and Jason Alexander (2007). In this approach, two
different features are emphasized: relatively simple cognitive
processes and structured interactions. Both have explored a variety of
games (such as the prisoner's dilemma, the stag hunt, divide the
dollar, and the ultimatum game) as exemplars of situations that offer
the possibility of the emergence of a moral norm. Though Skyrms
occasionally uses the replicator dynamic, both tend to emphasize
simpler mechanisms in an agent-based learning context. In particular,
learning rules like "imitate the best" or best response
are used, as they are much less cognitively demanding. Alexander
justifies the use of these simpler rules on the grounds that, rather
than fully rational agents, we are cognitively limited beings who rely
on fairly simple heuristics for our decision-making. Rules like
imitation are extremely simple to follow. Best response requires a bit
more cognitive sophistication, but is still simpler than a fully
Bayesian model with unlimited memory and computational power. These
simpler learning rules provide the same function as the replicator
dynamic: in between rounds of play, agents rely on their learning rule
to decide what strategy to employ. Note that both Skyrms and Alexander
tend to treat norms as single strategies.



The largest contribution of this strain of modeling comes not from the
assumption of boundedly rational agents, but rather the careful
investigation of the effects of particular social structures on the
equilibrium outcomes of various games. Much of the previous literature
on evolutionary games has focused on the assumptions of infinite
populations of agents playing games against randomly-assigned
partners. Skyrms and Alexander both rightly emphasize the importance
of structured interaction. As it is difficult to uncover and represent
real-world network structures, both tend to rely on examining
different classes of networks that have different properties, and from
there investigate the robustness of particular norms against these
alternative network structures. Alexander (2007) in particular has
done a very careful study of the different classical network
structures, where he examines lattices, small world networks, bounded
degree networks, and dynamic networks for each game and learning rule
he considers. A final feature of Skyrms and Alexander's work is
a refinement on this structural approach: they separate out two
different kinds of networks. First, there is the *interaction
network,* which represents the set of agents that any given agent
can actively play a game with. Second is the *update network*,
which is the set of agents that an agent can "see" when
applying her learning rule. The interaction network is thus
one's immediate community, whereas the update network is all
that the agent can see. To see why this is useful, we can imagine a
case not too different from how we live, in which there is a fairly
limited set of other people we may interact with, but thanks to a
plethora of media options, we can see much more widely how others
might act. This kind of situation can only be represented by clearly
separating the two networks.



Thus, what makes the theory of norm emergence of Skyrms and Alexander
so interesting is its enriching the set of idealizations that one must
make in building a model. The addition of structured interaction and
structured updates to a model of norm emergence can help make clear
how certain kinds of norms tend to emerge in certain kinds of
situation and not others, which is difficult or impossible to capture
in random interaction models.



Now that we have examined norm emergence, we must examine what happens
when a population is exposed to more than one social norm. In this
instance, social norms must compete with each other for adherents.
This lends itself to investigations about the competitive dynamics of
norms over long time horizons. In particular, we can investigate the
features of norms and of their environments, such as the populations
themselves, which help facilitate one norm becoming dominant over
others, or becoming prone to elimination by its competitors. An
evolutionary model provides a description of the conditions under
which social norms may spread. One may think of several environments
to start with. A population can be represented as entirely
homogeneous, in the sense that everybody is adopting the same type of
behavior, or heterogeneous to various degrees. In the former case, it
is important to know whether the commonly adopted behavior is stable
against mutations. The relevant concept here is that of an
*evolutionarily stable strategy* (ESS; Maynard Smith &
Price 1973; Taylor & Jonker 1978): when a population of
individuals adopts such a strategy, it cannot be successfully invaded
by isolated mutants, since the mutants will be at a disadvantage with
respect to reproductive success. An evolutionarily stable strategy is
a refinement of the Nash equilibrium in game theory. Unlike standard
Nash equilibria, evolutionarily stable strategies must either be
*strict equilibria*, or have an advantage when playing against
mutant strategies. Since strict equilibria are always superior to any
unilateral deviations, and the second condition requires that the ESS
have an advantage in playing against mutants, the strategy will remain
resistant to any mutant invasion. This is a difficult criterion to
meet, however. For example, a classic Tit-For-Tat strategy in the
prisoner's dilemma is not an ESS. Many strategies perform
equally well against it, including the very simple "Always
Cooperate" strategy, let alone Tit-For-Two-Tats, and any number
of variations. Tit-For-Tat is merely an evolutionarily neutral
strategy relative to these others. If we only consider strategies that
are defection-oriented, then Tit-For-Tat is an ESS, since it will do
better against itself, and no worse than defection strategies when
paired with them.



A more interesting case, and one relevant to a study of the
reproduction of norms of cooperation, is that of a population in which
several competing strategies are present at any given time. What we
want to know is whether the strategy frequencies that exist at a time
are stable, or if there is a tendency for one strategy to become
dominant over time. If we continue to rely on the ESS solution
concept, we see a classic example in the hawk-dove game. If we assume
that there is no uncorrelated asymmetry between the players, then the
mixed Nash equilibrium is the ESS. If we further assume that there is
no structure to how agents interact with each other, this can be
interpreted in two ways: either each player randomizes her strategy in
each round of play, or we have a stable polymorphism in the
population, in which the proportion of each strategy in the population
corresponds to the frequency with which each strategy would be played
in a randomizing approach. So, in those cases where we can assume that
players randomly encounter each other, whenever there is a mixed
solution ESS we can expect to find polymorphic populations.



If we wish to avoid the interpretive challenge of a mixed solution
ESS, there is an alternative analytic solution concept that we can
employ: the evolutionarily stable state. An evolutionarily stable
state is a distribution of (one or more) strategies that is robust
against perturbations, whether they are exogenous shocks or mutant
invasions, provided the perturbations are not overly large.
Evolutionarily stable states are solutions to a replicator dynamic.
Since evolutionarily stable states are naturally able to describe
polymorphic or monomorphic populations, there is no difficulty with
introducing population-oriented interpretations of mixed strategies.
This is particularly important when random matching does not occur, as
under those conditions, the mixed strategy can no longer be thought of
as a description of population polymorphism.



Now that we have seen the prominent approaches to both norm emergence
and norm stability, we can turn to some general interpretive
considerations of evolutionary models. An evolutionary approach is
based on the principle that strategies with higher current payoffs
will be retained, while strategies that lead to failure will be
abandoned. The success of a strategy is measured by its relative
frequency in the population at any given time. This is most easily
seen in a game theoretic framework. A game is repeated a finite number
of times with randomly selected opponents. After each round of the
game, the actual payoffs and strategies of the players become public
knowledge; on the basis of this information, each player adjusts her
strategy for the next round. The payoff to an individual player
depends on her choice as well as on the choices of the other players
in the game, and players are rational in the sense that they are
payoff-maximizers. In an evolutionary model, however, players learn
and adapt in a non-Bayesian way, that is, they do not condition on
past experience using Bayes' Rule. In this sense, they are not
typical rational learners (Nachbar 1990; Binmore & Samuelson
1992).



In an evolutionary approach behavior is adaptive, so that a strategy
that did work well in the past is retained, and one that fared poorly
will be changed. This can be interpreted in two ways: either the
evolution of strategies is the consequence of adaptation by individual
agents, or the evolution of strategies is understood as the
differential reproduction of agents based on their success rates in
their interactions. The former interpretation assumes short timescales
for interactions: many iterations of the game over time thus represent
no more than a few decades in time in total. The latter interpretation
assumes rather longer timescales: each instance of strategy adjustment
represents a new generation of agents coming into the population, with
the old generation dying simultaneously. Let us consider the
ramifications of each interpretation in turn.



In the first interpretation, we have agents who employ learning rules
that are less than fully rational, as defined by what a Bayesian agent
would have, both in terms of computational ability and memory. As
such, these rules tend to be classified as adaptive strategies: they
are reacting to a more limited set of data, with lower cognitive
resources than what a fully rational learner would possess. However,
there are many different adaptive mechanisms we may attribute to the
players. One realistic adaptive mechanism is learning by trial and
error; another plausible mechanism is imitation: those who do best are
observed by others who subsequently emulate their behavior (Hardin
1982). Reinforcement learning is another class of adaptive behavior,
in which agents tweak their probabilities of choosing one strategy
over another based on the payoffs they just received.



In the second interpretation, agents themselves do not learn, but
rather the strategies grow or shrink in the population according to
the reproductive advantages that they bestow upon the agents that
adhere to them. This interpretation requires very long timescales, as
it requires many generations of agents before equilibrium is reached.
The typical dynamics that are considered in such circumstances come
from biology. A standard approach is something like the replicator
dynamic. Norms grow or shrink in proportion to both how many agents
adhere to them at a given time, and their relative payoffs. More
successful strategies gain adherents at the expense of less-successful
ones. This evolutionary process assumes a constant-sized (or infinite)
population over time. This interpretation of an evolutionary dynamic,
which requires long timescales, raises the question of whether norms
themselves evolve slowly. Norms can rapidly collapse in a very short
amount of time. This phenomenon could not be represented within a
model whose interpretation is generational in nature. It remains an
open question, however, as to whether such timescales can be
appropriate for examining the emergence of certain kinds of norms.
While it is known that many norms can quickly come into being, it is
not clear if this is true of all norms.



Another challenge in using evolutionary models to study social norms
is that there is a potential problem of representation. In
evolutionary models, there is no rigorous way to represent innovation
or novelty. Whether we look at an agent-based simulation approach, or
a straightforward game-theoretic approach, the strategy set open to
the players, as well as their payoffs, must be defined in advance. But
many social norms rely on innovations, whether they are technological
or social. Wearing mini-skirts was not an option until they were
invented. Marxist attitudes were largely not possible until Marx. The
age at which one gets married and how many children one has are highly
linked to availability of and education about birth control
technologies. While much of the study of norms has focused on more
generic concepts such as fairness, trust, or cooperation, the full
breadth of social norms covers many of these more specific norms that
require some account of social innovation.



This representational challenge has broad implications. Even when we
can analytically identify evolutionarily stable states in a particular
game, which is suggestive of norms that will be converged upon, we now
have a problem of claiming that this norm has prospects for long-term
stability. Events like the publication of the Kinsey report can
dramatically shift seemingly stable norms quite rapidly. As the
underlying game changes in the representation, our previous results no
longer apply. In the face of this representational problem, we can
either attempt to develop some metric of the robustness of a given
norm in the space of similar games, or more carefully scope the claims
that we can make about the social norms that we study with this
methodology.



Although some questions of interpretation and challenges of
representation exist, an important advantage of the evolutionary
approach is that it does not require sophisticated strategic reasoning
in circumstances, such as large-group interactions, in which it would
be unrealistic to assume it. People are very unlikely to engage in
full Bayesian calculations in making decisions about norm adherence.
Agents often rely on cognitive shortcuts to determine when norms ought
to be in effect given a certain context, and whether or not they
should adhere to them. Evolutionary models that employ adaptive
learning strategies capture these kinds of cognitive constraints, and
allow the theorist to explore how these constraints influence the
emergence and stability of norms.


## 8. Conclusion



The study of social norms can help us understand a wide variety of
seemingly puzzling behaviors. According to some accounts, a social
norm results from conditional preferences for conforming to a relevant
behavioral rule. Such preferences are conditional on two different
kinds of beliefs: empirical and normative expectations.



This and other accounts of social norms still leave much to be
investigated. Explaining how normative expectations come to exist
remains an open question. Another open question to consider is how one
could intervene to change socially harmful norms. While there have
been initial investigations into these questions (Bicchieri 2016,
Muldoon 2018a, 2018b), there is much more work to be done. One
frontier in this area is in deploying behavioral tools such as nudging
for fostering norm changes (Bicchieri 2022, 2023).



Finally, we stress that different *contextual* factors (such as
the framing and characteristics of the strategic problem, the role one
is assigned, the social category with which one identifies, as well as
historical and chance events) often come to be associated with
different notions of "appropriate behavior". Accounting
for endogenous expectations is therefore key to a full understanding
of norm-driven behavior. More research--both theoretical and
experimental--is needed to further illuminate the impact of
expectations on strategic decisions.