The Strength of Weak Ties1
Mark S. Granovetter
Johns Hopkins University
Analysis of social networks is suggested as a tool for linking micro
and macro levels of sociological theory. The procedure is illustrated
by elaboration of the macro implications of one aspect of small-scale
interaction: the strength of dyadic ties. I t is argued that the degree
of overlap of two individuals' friendship networks varies directly
with the strength of their tie to one another. The impact of this
principle on diffusion of influence and information, mobility opportunity,
and community organization is explored. Stress is laid on the
cohesive power of weak ties. Most network models deal, implicitly,
with strong ties, thus confining their applicability to small, welldefined
groups. Emphasis on weak ties lends itself to discussion of
relations between groups and to analysis of segments of social structure
not easily defined in terms of primary groups.
A fundamental weakness of current sociological theory is that it does not
relate micro-level interactions to macro-level patterns in any convincing
way. Large-scale statistical, as well as qualitative, studies offer a good
deal of insight into such macro phenomena as social mobility, community
organization, and political structure. At the micro level, a large and increasing
body of data and theory offers useful and illuminating ideas about what
transpires within the confines of the small group. But how interaction in
small groups aggregates to form large-scale patterns eludes us in most cases.
I will argue, in this paper, that the analysis of processes in interpersonal
networks provides the most fruitful micro-macro bridge. In one way or
another, it is through these networks that small-scale interaction becomes
translated into large-scale patterns, and that these, in turn, feed back into
small groups.
Sociometry, the precursor of network analysis, has always been curiously
peripheral-invisible, really-in sociological theory. This is partly because
it has usually been studied and applied only as a branch of social psychology;
it is also because of the inherent complexities of precise network
analysis. We have had neither the theory nor the measurement and sampling
techniques to move sociometry from the usual small-group level to
that of larger structures. While a number of stimulating and suggestive
1This paper originated in discussions with Harrison White, to whom I am indebted
for many suggestions and ideas. Earlier drafts were read by Ivan Chase, James Davis,
William Michelson, Nancy Lee, Peter Rossi, Charles Tilly, and an anonymous referee;
their criticisms resulted in significant improvements.
1360 AJS Volume 78 Number 6
The Strength of Weak Ties
studies have recently moved in this direction (Bott 1957; Mayer 1961;
Milgram 1967; Boissevain 1968; Mitchell 1969), they do not treat structural
issues in much theoretical detail. Studies which do so usually involve
a level of technical complexity appropriate to such forbidding sources as
the Bulletin of Mathematical Biophysics, where the original motivation for
the study of networks was that of developing a theory of neural, rather
than social, interaction (see the useful review of this literature by Coleman
[ 19601; also Rapoport [ 1963] ) .
The strategy of the present paper is to choose a rather limited aspect of
small-scale interaction-the strength of interpersonal ties-and to show,
in some detail, how the use of network analysis can relate this aspect to
such varied macro phenomena as diffusion, social mobility, political organization,
and social cohesion in general. While the analysis is essentially
qualitative, a mathematically inclined reader will recognize the potential
for models; mathematical arguments, leads, and references are suggested
mostly in footnotes.
T H E STRENGTH OF TIES
Most intuitive notions of the "strength" of an interpersonal tie should be
satisfied by the following definition: the strength of a tie is a (probably
linear) combination of the amount of time, the emotional intensity, the
intimacy (mutual confiding), and the reciprocal services which characterize
the tie.2 Each of these is somewhat independent of the other, though the
set is obviously highly intracorrelated. Discussion of operational measures
of and weights attaching to each of the four elements is postponed to future
empirical s t ~ d i e s . ~ us canI t is sufficient for the present purpose if most of
agree, on a rough intuitive basis, whether a given tie is strong, weak, or
a b ~ e n t . ~
ZTies discussed in this paper are assumed to he positive and symmetric; a comprehensive
theory might require discussion of negative and/or asymmetric ties, but this
would add unnecessary complexity to the present, exploratory comments.
3 Some anthropologists suggest "multiplexity," that is, multiple contents in a relationship,
as indicating a strong tie (Kapferer 1969, p. 213). While this may be accurate
in some circumstances, ties with only one content or with diffuse content may be
strong as well (Simmel 1950, pp. 317-29). The present definition would show most
multiplex ties to he strong hut also allow for other possibilities.
"ncluded in "absent" are both the lack of any relationship and ties without substantial
significance, such as a "nodding" relationship between people living on the
same street, or the ''tie" to the vendor from whom one customarily buys a morning
newspaper. That two people "know" each other by name need not move their relation
out of this category if their interaction is negligible. In some contexts, however
(disasters, for example), such "negligible" ties might usefully be distinguished from
the absence of one. This is an ambiguity caused by substitution, for convenience of
exposition, of discrete values for an underlying continuous variable.
American Journal of Sociology
Consider, now, any two arbitrarily selected individuals-call them A and
B-and the set, S=C, D, E, ...,of all persons with ties to either or both
of them.5 The hypothesis which enables us to relate dyadic ties to larger
structures is: the stronger the tie between A and B, the larger the proportion
of individuals in S to whom they will both be tied, that is, connected
by a weak or strong tie. This overlap in their friendship circles is predicted
to be least when their tie is absent, most when it is strong, and intermediate
when it is weak.
The proposed relationship results, first, from the tendency (by definition)
of stronger ties to involve larger time commitments. If A-B and A-C ties
exist, then the amount of time C spends with B depends (in part) on the
amount A spends with B and C, respectively. (If the events "A is with B"
and "A is with C" were independent, then the event "C is with A and B"
would have probability equal to the product of their probabilities. For
example, if A and B are together 60% of the time, and A and C 40%,
then C, A, and B would be together 24% of the time. Such independence
would be less likely after than before B and C became acquainted.) If C
and B have no relationship, common strong ties to A will probably bring
them into interaction and generate one. Implicit here is Homans's idea that
"the more frequently persons interact with one another, the stronger their
sentiments of friendship for one another are apt to be" (1950, p. 133).
The hypothesis is made plausible also by empirical evidence that the
stronger the tie connecting two individuals, the more similar they are, in
various ways (Berscheid and Walster 1969, pp. 69-91; Bramel 1969,
pp. 9-16; Brown 1965, pp. 71-90; Laumann 1968; Newcomb 1961, chap.
5; Precker 1952). Thus, if strong ties connect A to B and A to C, both C
and B, being similar to A, are probably similar to one another, increasing
the likelihood of a friendship once they have met. Applied in reverse, these
two factors-time and similarity-indicate why weaker A-B and A-C ties
make a C-B tie less likely than strong ones: C and B are less likely to
interact and less likely to be compatible if they do.
The theory of cognitive balance, as formulated by Heider (1958) and
especially by Newcomb (1961, pp. 4-23), also predicts this result. If strong
ties A-B and A-C exist, and if B and C are aware of one another, anything
short of a positive tie would introduce a "psychological strain" into the
situation since C will want his own feelings to be congruent with those of
his good friend, A, and similarly, for B and his friend, A. Where the ties
are weak, however, such consistency is psychologically less crucial. (On
this point see also Homans [1950, p. 2551 and Davis [1963, p. 4481.)
Some direct evidence for the basic hypothesis exists (Kapferer 1969,
p. 229 n.; Laumann and Schuman 1967; Rapoport and Horvath 1961;
5 In Barnes's terminology, the union of their respective primary stars (1969, p. 58).
The Strength of Weak Ties
Rapoport 1963).6 This evidence is less comprehensive than one might hope.
In addition, however, certain inferences from the hypothesis have received
empirical support. Description of these inferences will suggest some of the
substantive implications of the above argument.
WEAK TIES I N DIFFUSION PROCESSES
To derive implications for large networks of relations, it is necessary to
frame the basic hypothesis more precisely. This can be done by investigating
the possible triads consisting of strong, weak, or absent ties among
A, B, and any arbitrarily chosen friend of either or both (i.e., some member
of the set S, described above). A thorough mathematical model would do
this in some detail, suggesting probabilities for various types. This analysis
becomes rather involved, however, and it is sufficient for my purpose in this
paper to say that the triad which is most unlikely to occur, under the
hypothesis stated above, is that in which A and B are strongly linked, A
has a strong tie to some friend C, but the tie between C and B is absent.
This triad is shown in figure 1. To see the consequences of this assertion,
FIG. 1.-Forbidden triad
I will exaggerate it in what follows by supposing that the triad shown never
occurs-that is, that the B-C tie is always present (whether weak or
strong), given the other two strong ties. Whatever results are inferred
from this supposition should tend to occur in the degree that the triad in
question tends to be absent.
6 The models and experiments of Rapoport and his associates have been a major stimulus
to this paper. In 1954 he commented on the 'Lwell-known fact that the likely
contacts of two individuals who are closely acquainted tend to be more overlapping
than those of two arbitrarily selected individuals" (p. 75). His and Horvath's 1961
hypothesis is even closer to mine: "one would expect the friendship relations, and
therefore the overlap bias of the acquaintance circles, to become less tight with increasing
numerical rank-order" (p. 290). (I.e., best friend, second-best friend, thirdbest,
etc.) Their development of this hypothesis, however, is quite different, substantively
and mathematically, from mine (Rapoport 1953a, 1953b, 1954, 1963; Rapoport
and Horvath 1961).
American Journal of Sociology
Some evidence exists for this absence. Analyzing 651 sociograms, Davis
(1970, p. 845) found that in 90% of them triads consisting of two mutual
choices and one nonchoice occurred less than the expected random number
of times. If we assume that mutual choice indicates a strong tie, this is
strong evidence in the direction of my a r g ~ m e n t . ~Newcomb (1961, pp. 160-
65) reports that in triads consisting of dyads expressing mutual "high
attraction," the configuration of three strong ties became increasingly
frequent as people knew one another longer and better; the frequency of
the triad pictured in figure 1 is not analyzed, but it is implied that processes
of cognitive balance tended to eliminate it.
The significance of this triad's absence can be shown by using the
concept of a "bridge"; this is a line in a network which provides the only
path between two points (Harary, Norman, and Cartwright 1965, p. 198).
Since, in general, each person has a great many contacts, a bridge between
A and B provides the only route along which information or influence can
flow from any contact of A to any contact of B, and, consequently, from
anyone connected indirectly to A to anyone connected indirectly to B. Thus,
in the study of diffusion, we can expect bridges to assume an important
role.
Now, if the stipulated triad is absent, it follows that, except under unlikely
conditions, no strong tie is a bridge. Consider the strong tie A-B: if A
has another strong tie to C, then forbidding the triad of figure 1 implies
that a tie exists between C and B, so that the path A-C-B exists between A
and B ; hence, A-B is not a bridge. A strong tie can be a bridge, therefore,
only if neither party to it has any other strong ties, unlikely in a social
network of any size (though possible in a small group). Weak ties suffer no
such restriction, though they are certainly not automatically bridges. What
is important, rather, is that all bridges are weak ties.
In large networks it probably happens only rarely, in practice, that a
specific tie provides the only path between two points. The bridging function
may nevertheless be served locally. In figure 2a, for example, the tie
A-B is not strictly a bridge, since one can construct the path A-E-I-B (and
others). Yet, A-B is the shortest route to B for F , D, and C. This function
is clearer in figure 2b. Here, A-B is, for C, D, and others, not only a local
bridge to B, but, in most real instances of diffusion, a much more likely
and efficient path. Harary et al. point out that "there may be a distance
[length of path] beyond which it is not feasible for u to communicate with
7This assumption is suggested by one of Davis's models (1970, p. 846) and made
explicitly by Mazur (1971). It is not obvious, however. In a free-choice sociometric
test or a fixed-choice one with a large number of choices, most strong ties would
probably result in mutual choice, but some weak ones might as well. With a small,
fixed number of choices, most mutual choices should be strong ties, but some strong
ties might show up as asymmetric. For a general discussion of the biases introduced
by sociometric procedures, see Holland and Leinhardt ( 1 9 7 1 b ) .
The Strength of Weak Ties
FIG.2.-Local bridges. a, Degree 3 ; b, Degree 13. -=strong tie ; ---=
weak tie.
v because of costs or distortions entailed in each act of transmission. If v
does not lie within this critical distance, then he will not receive messages
originating with u" (1965, p. 159). I will refer to a tie as a "local bridge
of degree n" if n represents the shortest path between its two points (other
than itself), and n > 2. In figure 2a, A-B is a local bridge of degree 3, in
26, of degree 13. As with bridges in a highway system, a local bridge in a
social network will be more significant as a connection between two sectors
to the extent that it is the only alternative for many people-that is, as its
degree increases. A bridge in the absolute sense is a local one of infinite
degree. By the same logic used above, only weak ties may be local bridges.
Suppose, now, that we adopt Davis's suggestion that "in interpersonal
flows of most any sort the probability that 'whatever it is' will flow from
person i to person j is (a) directly proportional to the number of all-positive
(friendship) paths connecting i and j; and ( b ) inversely proportional to
the length of such paths" (1969, p. 549).8 The significance of weak ties,
then, would be that those which are local bridges create more, and shorter,
paths. Any given tie may, hypothetically, be removed from a network; the
number of paths broken and the changes in average path length resulting
8Though this assumption seems plausible, it is by no means self-evident. Surprisingly
little empirical evidence exists to support or refute it.
American Journal of Sociology
between arbitrary pairs of points (with some limitation on length of path
considered) can then be computed. The contention here is that removal of
the average weak tie would do more "damage" to transmission probabilities
than would that of the average strong one?
Intuitively speaking, this means that whatever is to be diffused can reach
a larger number of people, and traverse greater social distance (i.e., path
length),1° when passed through weak ties rather than strong. If one tells
a rumor to all his close friends, and they do likewise, many will hear the
rumor a second and third time, since those linked by strong ties tend to
share friends. If the motivation to spread the rumor is dampened a bit on
each wave of retelling, then the rumor moving through strong ties is much
more likely to be limited to a few cliques than that going via weak ones;
bridges will not be crossed.ll
Since sociologists and anthropologists have carried out many hundreds of
diffusion studies-Rogers's 1962 review dealt with 506--one might suppose
that the above claims could easily be put to test. But this is not so, for
several reasons. To begin with, though most diffusion studies find that
personal contacts are crucial, many undertake no sociometric investigation.
(Rogers [I9621 discusses this point.) When sociometric techniques are
used, they tend to discourage the naming of those weakly tied to the
respondent by sharply limiting the numbers of choices allowed. Hence, the
proposed importance of weak ties in diffusion is not measured. Even when
more sociometric information is collected there is almost never an attempt
to directly retrace the exact interpersonal paths traversed by an (idea,
rumor, or) innovation. More commonly, the time when each individual
adopted the innovation is recorded, as is the number of sociometric choices
he received from others in the study. Those receiving many choices are
characterized as "central," those with few as "marginal"; this variable is
then correlated with time of adoption and inferences made about what paths
were probably followed by the innovation.
9 In a more comprehensive treatment it would be useful to consider to what extent a
set of weak ties may be considered to have bridging functions. This generalization
requires a long, complex discussion and is not attempted here (see Harary et al. 1965,
pp. 211-16).
10 We may define the "social distance" between two individuals in a network as the
number of lines in the shortest path from one to another. This is the same as the
definition of "distance" between points in graph theory (Harary et al. 1965, pp. 32-33,
138-41). The exact role of this quantity in diffusion and epidemic theory is discussed
by Solomonoff and Rapoport (1951).
11If a damping effect is not specified, the whole population would hear the rumor
after a sufficiently large number of retellings, since few real networks include totally
self-contained cliques. The effective difference Between using weak and strong ties,
then, is one of people reached per unit of (ordinal) time. This could be called
"velocity" of transmission. I am indebted to Scott Feld for this point.
The Strength of Weak Ties
One point of controversy in diffusion studies can be related to my
argument. Some have indicated that early innovators are marginal, that
they "underconform to norms to such a degree that they are perceived
as highly deviant" (Rogers 1962, p. 197). Others (e.g., Coleman, Katz,
and Menzel [I9661 on the adoption of a new drug by doctors) find that
those named more frequently adopt an innovation substantially earlier.
Becker (1970) tries to resolve the question of whether early innovators
are "central" or "marginal" by referring to the "perceived risks of adoption
of a given innovation." His study of public health innovations shows that
when a new program is thought relatively safe and uncontroversial (as with
the drug of Coleman et al.), central figures lead in its adoption; otherwise,
marginal ones do (p. 273). He explains the difference in terms of a greater
desire of "central" figures to protect their professional reputation.
Kerckhoff, Back, and Miller (1965) reach a similar conclusion in a
different type of study. A Southern textile plant had been swept by "hysterical
contagion": a few, then more and more workers, claiming bites
from a mysterious "insect," became nauseous, numb, and weak, leading to
a plant shutdown. When the affected workers were asked to name their
three best friends, many named one another, but the very earliest to be
stricken were social isolates, receiving almost no choices. An explanation,
compatible with Becker's, is offered: since the symptoms might be thought
odd, early "adopters" were likely to be found among the marginal, those
less subject to social pressures. Later, "it is increasingly likely that some
persons who are socially integrated will be affected. . . . The contagion
enters social networks and is disseminated with increasing rapidity" (p. 13).
This is consistent with Rogers's comment that while the first adopters of
innovations are marginal, the next group, ('early adopters," "are a more
integrated part of the local social system than the innovators" (1962, p.
183).
"Central" and "marginal" individuals may well be motivated as claimed;
but if the marginal are genuinely so, it is difficult to see how they can ever
spread innovations successfully. We may surmise that since the resistance
to a risky or deviant activity is greater than to a safe or normal one, a larger
number of people will have to be exposed to it and adopt it, in the early
stages, before it will spread in a chain reaction. Individuals with many
weak ties are, by my arguments, best placed to diffuse such a difficult innovation,
since some of those ties will be local bridges.12 An initially un-
12 These individuals are what is often called, in organizational analysis, "liaison persons,"
though their role here is different from the one usually discussed. (Cf. the concept in
graph theory of a "cut pointn-one which, if removed from a graph, disconnects one
part from another [Harary 19651.) In general, a bridge has one liaison person on each
side, but the existence of a liaison person does not imply that of a bridge. For local
American Journal of Sociology
popular innovation spread by those with few weak ties is more likely to be
confined to a few cliques, thus being stillborn and never finding its way
into a diffusion study.
That the "marginal" innovators of diffusion studies might actually be
rich in weak ties is possible, given the usual sociometric technique, but in
most cases this is purely speculative. Kerckhoff and Back, however, in a
later more detailed analysis of the hysteria incident, indicate that besides
asking about one's "three best friends," they also asked with whom
workers ate, worked, shared car pools, etc. They report that five of the six
workers earliest affected "are social isolates when friendship choices are
used as the basis of analysis. Only 1 of the 6 is mentioned as a friend by
anyone in our sample. This is made even more striking when we note that
these 6 women are mentioned with considerable frequency when other bases
for choice are used. In fact, they are chosen more frequently on a 'nonfriendship'
basis than are the women in any of the other categories" (1968,
p. 112).
This finding lends credence to the weak-tie argument, but is inconclusive.
A somewhat different kind of diffusion study offers more direct support:
the "small-world" investigations of Milgram and his associates. The name
of these studies stems from the typical comment of newly introduced individuals
who discover some common acquaintance; this situation is generalized
in an attempt to measure, for arbitrarily chosen pairs of individuals
in the United States, how long a path of personal contacts would be needed
to connect them. A booklet is given to randomly designated senders who
are asked to forward it toward some named target person, via someone the
sender knows personally who would be more likely than himself to know
the target. The new recipient then advances the booklet similarly; eventually
it reaches the target or someone fails to send it on. The proportion of
such chains completed has ranged from 12% to 33% in different studies,
and the number of links in completed chains has ranged from two to 10,
averaging between five and eight (Milgram 1967; Travers and Milgram
1969; Korte and Milgram 1970).
Each time someone forwards a booklet he also sends a postcard to the
researchers, indicating, among other things, the relationship between himself
and the next receiver. Two of the categories which can be chosen are
"friend" and "acquaintance." I will assume that this corresponds to
"strong" and "weak" ties. In one of the studies, white senders were asked
to forward the booklet to a target who was Negro. In such chains, a crucial
point was the first sending of the booklet from a white to a Negro. In 50%
bridges, the concept of local liaisons could be developed. In a more microscopically
oriented discussion I would devote more time to the liaison role. For now, I only point
out that, under the present assumptions, one can be a liaison between two network
sectors only if all his ties into one or both are weak.
The Strength of Weak Ties
of the instances where the white described this Negro as an "acquaintance,"
the chain was ultimately completed; completion rate fell to 2676, however,
when the white sent the booklet to a Negro "friend." (My computation,
based on unpublished data kindly supplied by Charles Korte. See Korte
[I9671 and Korte and Milgram [I9701.) Thus, weaker interracial ties can
be seen to be more effective in bridging social distance.
Another relevant study, by Rapoport and Horvath (1961)) is not exactly
one of diffusion but is closely related in that it traces out paths along
which diffusion could take place. They asked each individual in a Michigan
junior high school (N =851) to list his eight best friends in order of preference.
Then, taking a number of random samples from the group (sample
size, an arbitrary number, was nine), they traced out, for each sample, and
averaged over all the samples, the total number of people reached by following
along the network of first and second choices. That is, the first and
second choices of each sample member were tabulated, then the first and
second choices of these people were added in, etc., counting, at each remove,
only names not previously chosen, and continuing until no new people were
reached. The same procedure was followed using second and third choices,
third and fourth, etc., up to seventh and eighth. (The theoretical connection
of this tracing procedure to diffusion is discussed by Rapoport [1953a,
19533, and especially 19541.)
The smallest total number of people were reached through the networks
generated by first and second choices-presumably the strongest ties-and
the largest number through seventh and eighth choices. This corresponds
to my assertion that more people can be reached through weak ties. A
parameter in their mathematical model of the sociogram, designed to measure,
approximately, the overlap of acquaintance circles, declined monotonically
with increasing rank order of friends.13
WEAK TIES IN EGOCENTRIC NETWORKS
I n this section and the next, I want to discuss the general significance of
the above findings and arguments at two levels: first that of individuals,
then that of communities. These discussions make no pretense of being
comprehensive; they are meant only to illustrate possible applications.
In recent years, a great deal of literature has appeared analyzing the
impact on the behavior of individuals of the social networks in which they
are imbedded. Some of the studies have emphasized the ways in which
13This parameter, 0, measures such overlap in the following sense: it is zero in a
random net-one in which individuals choose others at random-and is one in a net
made up entirely of cliques disconnected each from every other. Intermediate values of
0, however, do not have a good intuitive interpretation in terms of individuals, but
only with reference to the particular mathematical model defining the parameter; thus
it does not correspond precisely to my arguments about friendship overlap.
American Journal of Sociology
behavior is shaped and constrained by one's network (Bott 1957; Mayer
1961; Frankenberg 1965)) others the ways in which individuals can
manipulate these networks to achieve specific goals (Mayer 1966; Boissevain
1968; Kapferer 1969). Both facets are generally supposed to be
affected by the structure of one's network. Bott argued that the crucial
variable is that of whether one's friends tend to know one another ("closeknit"
network) or not ("loose-knit" network). Barnes makes this dichotomy
into a continuous variable by counting the number of ties observed
in the network formed by ego and his friends and dividing it by the ratio
of possible ones; this then corresponds to what is often called network
"density" (Barnes 1969; Tilly 1969).14
Epstein (1969) points out, however, that different parts of ego's network
may have different density. He calls those with whom one "interacts most
intensely and most regularly, and who are therefore also likely to come to
know one another," the "effective network"; the "remainder constitute
the extended network" (pp. 110-1 1) .This is close to saying, in my terms,
that one's strong ties form a dense network, one's weak ties a less dense one.
I would add that one's weak ties which are not local bridges might as well
be counted with the strong ties, to maximize separation of the dense from
the less dense network sectors.
One point on which there is no general agreement is whether ego's network
should be treated as composed only of those to whom he is tied
directly, or should include the contacts of his contacts, and/or others.
Analyses stressing encapsulation of an individual by his network tend to
take the former position, those stressing manipulation of networks, the
latter, since information or favors available through direct contacts may
depend on who their contacts are. I would argue that by dividing ego's
network into that part made up of strong and nonbridging weak ties on
the one hand, and that of bridging weak ties on the other, both orientations
can be dealt with. Ties in the former part should tend to be to people who
not only know one another, but who also have few contacts not tied to ego
as well. In the "weak" sector, however, not only will ego's contacts not be
tied to one another, but they will be tied to individuals not tied to ego.
Indirect contacts are thus typically reached through ties in this sector;
such ties are then of importance not only in ego's manipulation of networks,
but also in that they are the channels through which ideas, influences, or
14But if the crucial question is really whether ego's friends know each other, this
measure should probably be computed after ego and his ties have been subtracted from
the network; distortions caused by failure to do so will be especially great in small
networks. It is important to note, also, that in nonegocentric networks, there is no
simple correspondence between density and any "average" measure of the extent to
which the various egos have friends who know one another. "Density," as used here,
should not be confused with the ''axone density" of Rapoport's models-the number
of choices issuing from each node of a network.
The Strength of Weak Ties
information socially distant from ego may reach him. The fewer indirect
contacts one has the more encapsulated he will be in terms of knowledge of
the world beyond his own friendship circle; thus, bridging weak ties (and
the consequent indirect contacts) are important in both ways.
I will develop this point empirically by citing some results from a labormarket
study I have recently completed. Labor economists have long been
aware that American blue-collar workers find out about new jobs more
through personal contacts than by any other method. (Many studies are
reviewed by Parnes 1954, chap. 5.) Recent studies suggest that this is
also true for those in professional, technical, and managerial positions
(Shapero, Howell, and Tombaugh 1965; Brown 1967; Granovetter 1970).
My study of this question laid special emphasis on the nature of the tie
between the job changer and the contact person who provided the necessary
information.
In a random sample of recent professional, technical, and managerial job
changers living in a Boston suburb, I asked those who found a new job
through contacts how often they saw the contact around the time that he
passed on job information to them. I will use this as a measure of tie
strength.15 A natural a priori idea is that those with whom one has strong
ties are more motivated to help with job information. Opposed to this
greater motivation are the structural arguments I have been making: those
to whom we are weakly tied are more likely to move in circles different
from our own and will thus have access to information different from that
which we receive.
I have used the following categories for frequency of contact: often =at
least twice a week; occasionally =more than once a year but less than twice
a week; rarely =once a year or less. Of those finding a job through contacts,
16.7% reported that they saw their contact often at the time, 55.6%
said occasionally, and 27.8% rarely (N = 54).I6 The skew is clearly to the
weak end of the continuum, suggesting the primacy of structure over
motivation.
In many cases, the contact was someone only marginally included in the
current network of contacts, such as an old college friend or a former workmate
or employer, with whom sporadic contact had been maintained
15 Although this corresponds only to the first of the four dimensions in my definition,
supplementary anecdotal evidence from interviews makes it likely that, in this case,
the entire definition is satisfied by this measure. At the time of research, it had not
occurred to me that tie strength would be a useful variable.
16The numbers reported are small because they represent a random subsample of 100,
who were interviewed personally, of the total sample of 282. The personal interview
allowed more detailed questioning. Comparisons between the mail sample and the
interview sample on the large number of items which were put to both show almost no
significant differences; this suggests that results observed in the smaller sample on
those items put to it alone would not be much different in the mail sample.
American Journal of Sociology
(Granovetter 1970, pp. 76-80). Usually such ties had not even been very
strong when first forged. For work-related ties, respondents almost invariably
said that they never saw the person in a nonwork context.17 Chance
meetings or mutual friends operated to reactivate such ties. It is remarkable
that people receive crucial information from individuals whose very existence
they have forgotten.ls
I also asked respondents where their contacts got the information they
transmitted. I n most cases, I traced the information to its initial source.
I had expected that, as in the diffusion of rumors or diseases, long paths
would be involved. But in 39.1% of the cases information came directly
from the prospective employer, whom the respondent already knew; 45.3%
said that there was one intermediary between himself and the employer;
12.5% reported two; and 3.1% more than two (N =64). This suggests
that for some important purposes it may be sufficient to discuss, as I have,
the egocentric network made up of ego, his contacts, and their contacts.
Had long information paths been involved, large numbers might have found
out about any given job, and no particular tie would have been crucial.
Such a model of job-information flow actually does correspond to the
economists' model of a "perfect" labor market. But those few who did
acquire information through paths with more than one intermediary tended
to be young and under the threat of unemployment; influence was much
less likely to have been exerted by their contact on their behalf. These
respondents were, in fact, more similar to those using formal intermediaries
(agencies, advertisements) than to those hearing through short paths:
both of the former are badly placed and dissatisfied in the labor market,
and both receive information without influence. Just as reading about a
job in the newspaper affords one no recommendation in applying for it,
neither does it to have heard about it fifth hand.
The usual dichotomy between "formal" or mass procedures and diffusion
through personal contacts may thus be invalid in some cases where, instead,
the former may be seen as a limiting case of long diffusion chains. This is
17 Often when I asked respondents whether a friend had told them about their current
job, they said, "Not a friend, an acquaintance." I t was the frequency of this comment
which suggested this section of the paper to me.
18 Donald Light has suggested to me an alternative reason to expect predominance of
weak ties in transfer of job information. He reasons that most of any given person's
ties are weak, so that we should expect, on a "random" model, that most ties through
which job information flows should be weak. Since baseline data on acquaintance
networks are lacking, this objection remains inconclusive. Even if the premise were
correct, however, one might still expect that greater motivation of close friends
would overcome their being outnumbered. Different assumptions yield different
"random" models; it is not clear which one should be accepted as a starting point. One
plausible such model would expect information to flow through ties in proportion to
the time expended in interaction; this model would predict much more information
via strong ties than one which merely counted all ties equally.
The Strength of Weak Ties
especially likely where information of instrumental significance is involved.
Such information is most valuable when earmarked for one person.
From the individual's point of view, then, weak ties are an important
resource in making possible mobility opportunity. Seen from a more macroscopic
vantage, weak ties play a role in effecting social cohesion. When a
man changes jobs, he is not only moving from one network of ties to
another, but also establishing a link between these. Such a link is often of
the same kind which facilitated his own movement. Especially within professional
and technical specialties which are well defined and limited in size,
this mobility sets up elaborate structures of bridging weak ties between
the more coherent clusters that constitute operative networks in particular
locations. Information and ideas thus flow more easily through the specialty,
giving it some "sense of community," activated at meetings and
conventions. Maintenance of weak ties may well be the most important
consequence of such meetings.
WEAK TIES AND COMMUNITY ORGANIZATION
These comments about sense of community may remind us that in many
cases it is desirable to deal with a unit of analysis larger than a single
individual. I would like to develop my argument further by analyzing, in
this section, why some communities organize for common goals easily and
effectively whereas others seem unable to mobilize resources, even against
dire threats. The Italian community of Boston's West End, for example,
was unable to even form an organization to fight against the "urban renewal"
which ultimately destroyed it. This seems especially anomalous in
view of Gans's description of West End social structure as cohesive (1962).
Variations in culture and personality are often cited to explain such
iAclnalies. Gans contrasts "lowern-, "workingn-, and "middlen-class subcultures,
concluding that only the last provides sufficient trust in leaders
and practice in working toward common goals to enable formation of an
effective organization. Thus, the working-class West End could not resist
urban renewal (pp. 229-304). Yet, numerous well-documented cases show
that some working-class communities have mobilized quite successfully
against comparable or lesser threats (Dahl 1961, pp. 192-99; Keyes 1969;
Davies 1966, chap. 4).19 I would suggest, as a sharper analytical tool,
examination of the network of ties comprising a community to see whether
aspects of its structure might facilitate or block organization.
Imagine, to begin with, a community completely partitioned into cliques,
such that each person is tied to every other in his clique and to none outside.
Community organization would be severely inhibited. Leafletting, radio
announcements, or other methods could insure that everyone was aware of
1QThis point was brought to my attention by Richard Wolfe.
American Journal of Sociology
some nascent organization; but studies of diffusion and mass communication
have shown that people rarely act on mass-media information unless
it is also transmitted through personal ties (Katz and Lazarsfeld 1955;
Rogers 1962); otherwise one has no particular reason to think that an
advertised product or an organization should be taken seriously. Enthusiasm
for an organization in one clique, then, would not spread to others
but would have to develop independently in each one to insure success.
The problem of trust is closely related. I would propose that whether a
person trusts a given leader depends heavily on whether there exist intermediary
personal contacts who can, from their own 'knowledge, assure him
that the leader is trustworthy, and who can, if necessary, intercede with
the leader or his lieutenants on his behalf. Trust in leaders is integrally
related to the capacity to predict and affect their behavior. Leaders, for
their part, have little motivation to be responsive or even trustworthy
toward those to whom they have no direct or indirect connection. Thus,
network fragmentation, by reducing drastically the number of paths from
any leader to his potential followers, would inhibit trust in such leaders.
This inhibition, furthermore, would not be entirely irrational.
Could the West End's social structure really have been of this kind?
Note first that while the structure hypothesized is, by definition, extremely
fragmented, this is evident only at a macroscopic level-from an "aerial
view" of the network. The local phenomenon is cohesion. (Davis [I9671
also noted this paradox, in a related context.) An analyst studying such a
group by participant observation might never see the extent of fragmentation,
especially if the cliques were not earmarked by ethnic, cultural, or
other visible differences. In the nature of participant observation, one is
likely to get caught up in a fairly restricted circle; a few useful contacts
are acquired and relied on for introduction to others. The "problem of
entry into West End society was particularly vexing," Gans writes. But
eventually, he and his wife "were welcomed by one of our neighbors and
became friends with them. As a result they invited us to many of their
evening gatherings and introduced us to other neighbors, relatives and
friends. . . .As time went on . . . other West Enders . . .introduced me to
relatives and friends, although most of the social gatherings at which I
participated were those of our first contact and their circle" (1962, pp. 340-
41; emphasis supplied). Thus, his account of cohesive groups is not inconsistent
with overall fragmentation.
Now, suppose that all ties in the West End were either strong or absent,
and that the triad of figure 1 did not occur. Then, for any ego, all his
friends were friends of one another, and all their friends were ego's friends
as well. Unless each person was strongly tied to all others in the community,
network structure did indeed break down into the isolated cliques posited
above. (In terms of Davis's mathematical treatment, the overall network
The Strength of Weak Ties
was "clusterable," with unique clusters [1967, p. 1861.) Since it is unlikely
that anyone could sustain more than a few dozen strong ties, this would,
in fact, have been the result.
Did strong ties take up enough of the West Enders' social time to make
this analysis even approximately applicable? Gans reported that "sociability
is a routinized gathering of a relatively unchanging peer group of family
members and friends that takes place several times a week." Some "participate
in informal cliques and in clubs made up of unrelated people. . . .
In number, and in the amount of time devoted to them, however, these
groups are much less important than the family circle" (1962, pp. 74, 80).
Moreover, two common sources of weak ties, formal organizations and
work settings, did not provide them for the West End; organization membership
was almost nil (pp. 104-7) and few worked within the area itself,
so that ties formed at work were not relevant to the community (p. 122).
Nevertheless, in a community marked by geographic immobility and
lifelong friendships (p. 19) it strains credulity to suppose that each person
would not have known a great many others, so that there would have been
some weak ties. The question is whether such ties were bridges.20 If none
were, then the community would be fragmented in exactly the same way
as described above, except that the cliques would then contain weak as
well as strong ties. (This follows, again, from Davis's analysis of "clusterability,"
with strong and weak ties called "positive" and absent ones
"negative" [1967].) Such a pattern is made plausible by the lack of ways
in the West End to develop weak ties other than by meeting friends of
friends (where "friend" includes relatives)-in which case the new tie is
automatically not a bridge. I t is suggested, then, that for a community to
have many weak ties which bridge, there must be several distinct ways or
contexts in which people may form them. The case of Charlestown, a
working-class community which successfully organized against the urban
renewal plan of the same city (Boston) against which the West End was
powerless, is instructive in this respect: unlike the West End, it had a
rich organizational life, and most male residents worked within the area
(Keyes 1969, chap. 4).
In the absence of actual network data, all this is speculation. The hard
information needed to show either that the West End was fragmented or
that communities which organized successfully were not, and that both
patterns were due to the strategic role of weak ties, is not at hand and
would not have been simple to collect. Nor has comparable information
been collected in any context. But a theoretical framework has, at least,
been suggested, with which one could not only carry out analyses post hoc,
but also predict differential capacity of communities to act toward common
20 See Jane Jacobs's excellent, intuitive, discussion of bridging ties ("hop-skip links")
in community organization (1961, chap. 6.)
American Journal of Sociology
goals. A rough principle with which to begin such an investigation might
be: the more local bridges (per person?) in a community and the greater
their degree, the more cohesive the community and the more capable of
acting in concert. Study of the origins and nature (strength and content,
for example) of such bridging ties would then offer unusual insight into
the social dynamics of the community.
MICRO AND MACRO NETWORK MODELS
Unlike most models of interpersonal networks, the one presented here is
not meant primarily for application to small, face-to-face groups or to
groups in confined institutional or organizational settings. Rather, it is
meant for linkage of such small-scale levels with one another and with
larger, more amorphous ones. This is why emphasis here has been placed
more on weak ties than on strong. Weak ties are more likely to link members
of diflerent small groups than are strong ones, which tend to be
concentrated within particular groups.
For this reason, my discussion does not lend itself to elucidation of the
internal structure of small groups. This point can be made more clearly by
contrasting the model of this paper to one with which it shares many
similarities, that of James Davis, Paul Holland, and Samuel Leinhardt
(hereafter, the DHL model) (Davis 1970; Davis and Leinhardt 1971;
Holland and Leinhardt 1970, 197la, 19716; Davis, Holland, and Leinhardt
1971; Leinhardt 1972). The authors, inspired by certain propositions in
George Homans's The Human Group ( 1950), argue that "the central proposition
in structural sociometry is this: Interpersonal choices tend to be
transitive-if P chooses 0 and 0 chooses X, then P is likely to choose X"
(Davis et al. 1971, p. 309). When this is true without exception, a sociogram
can be divided into cliques in which every individual chooses every
other; any asymmetric choices or nonchoices are between such cliques, and
asymmetry, if present, runs only in one direction. A partial ordering of
cliques may thus be inferred. If mutual choice implies equal, and assymmetric
choice unequal, status, then this ordering reflects the stratification
structure of the group (Holland and Leinhardt 1971a, pp. 107-14).
One immediate difference between this model and mine is that it is cast
in terms of "choices" rather than ties. Most sociometric tests ask people
whom they like best or would prefer to do something with, rather than with
whom they actually spend time. If transitivity is built more into our cognitive
than our social structure, this method might overstate its prevalence.
But since the DHL model could recast in terms of ties, this is not a conclusive
difference.
More significant is the difference in the application of my argument to
transitivity. Let P choose 0 and 0 choose X (or equivalently, let X choose
The Strength of Weak Ties
0 and 0 choose P ) : then I assert that transitivity-P choosing X (or X,
P)-is most likely when both ties-P-0 and 0-X-are strong, least likely
when both are weak, and of intermediate probability if one is strong and
one weak. Transitivity, then, is claimed to be a function of the strength
of ties, rather than a general feature of social structure.
The justification of this assertion is, in part, identical with that offered
earlier for the triad designated A-B-C. In addition, it is important to point
out here that the DHL model was designed for small groups, and with
increasing size of the group considered the rationale for transitivity
weakens. If P chooses 0 and 0 chooses X, P should choose X out of consistency;
but if P does not know or barely knows X, nonchoice implies no
inconsistency. For the logic of transitivity to apply, a group must be small
enough so that any person knows enough about every other person to be
able to decide whether to "choose" him, and encounters him often enough
that he feels the need for such a decision. Including weak ties in my model,
then, lessens the expectation of transitivity and permits analysis of intergroup
relationships and also of amorphous chunks of social structure which
an analyst may ferret out as being of interest, but which are not easily
defined in terms of face-to-face groups. Anthropologists have recently referred
to such chunks as "quasi-groups" (Mayer 1966; Boissevain 1968).
Since, as I have argued above, weak ties are poorly represented in sociograms,
there is little in the DHL empirical studies-which apply statistical
tests to sociometric data-to confirm or disconfirm my argument on transitivity.
One finding does lend itself to speculation, however. Leinhardt
(1972) shows that the sociograms of schoolchildren conform more and
more closely to the transitive model as they become older, sixth graders
being the oldest tested. He interprets this as reflecting cognitive development-increasing
capacity to make use of transitive logic. If my assertion
is correct, an alternative possibility would be that children develop stronger
ties with increasing age. This is consistent with some theories of child
development (see especially Sullivan 1953, chap. 16) and would imply, on
my argument, greater transitivity of structure. Some support for this explanation
comes from Leinhardt's finding that proportion of choices which
were mutual was positively correlated with both grade level and degree of
transitivity. In these sociograms, with an average of only about four choices
per child, it seems likely that most mutual choices reflected strong ties
(see n. 7, above).
CONCLUSION
The major implication intended by this paper is that the personal experience
of individuals is closely bound up with larger-scale aspects of social
structure, well beyond the purview or control of particular individuals.
American Journal of Sociology
Linkage of micro and macro levels is thus no luxury but of central importance
t o the development of sociological theory. such linkage generates
paradoxes: weak ties, often denounced as generative of alienation (Wirth
1938) are here seen as indispensable to individuals' opportunities and to
their integration into communities; strong ties, breeding local cohesion,
lead to overall fragmentation. Paradoxes are a welcome antidote to theories
which explain everything all too neatly.
The model offered here is a very limited step in the linking of levels; it
is a fragment of a theory. Treating only the strength of ties ignores, for
instance, all the important issues involving their content. What is the relation
between strength and degree of specialization of ties, or between
strength and hierarchical structure? How can "negative" ties be handled?
Should tie strength be developed as a continuous variable? What is the
developmental sequence of network structure over time?
As such questions are resolved, others will arise. Demography, coalition
structure, and mobility are just a few of the variables which would be of
special importance in developing micro-macro linkage with the help of
network analysis; how these are related to the present discussion needs
specification. My contribution here is mainly, then, exploratory and programmatic,
its primary purpose being to generate interest in the proposed
program of theory and research.
REFERENCES
Barnes, J. A. 1969. "Networks and Political Process." In Social Networks in Urban
Situations, edited by J. C. Mitchell. Manchester: Manchester University Press.
Becker, Marshall. 1970. "Sociometric Location and Innovativeness." American Sociological
Review 35 (April) : 267-82.
Berscheid, E., and E. Walster. 1969. Interpersonal Attraction. Reading, Mass.: Addison-
Wesley.
Boissevain, J. 1968. "The Place of Non-Groups in the Social Sciences." Man 3
(December) : 542-56.
Bott, Elizabeth. 1957. Family and Social Network. London: Tavistock.
Bramel, D. 1969. "Interpersonal Attraction, Hostility and Perception." In Experimental
Social Psychology, edited by Judson Mills. New York: Macmillan.
Brown, David. 1967. The Mobile Professors. Washington, D.C.: American Council
on Education.
Brown, Roger. 1965. Social Psychology. New York: Free Press.
Coleman, J. S. 1960. "The Mathematical Study of Small Groups." In Mathematical
Thinking in the Measurement of Behavior, edited by H. Solomon. Glencoe: Free
Press.
Coleman, J. S., E. Katz, and H. Menzel. 1966. Medical Innovation: A Diffusion Study.
Indianapolis: Bobbs-Merrill.
Dahl, Robert. 1961. Who Governs? New Haven, Conn.: Yale University Press.
Davies, J. C. 1966. iVeighborhood Groups and Urban Renewal. New York: Columbia
University Press.
Davis, James A. 1963. "Structural Balance, Mechanical Solidarity and Interpersonal
Relations." American Journal of Sociology 68 (January): 444-62.
-. 1967. "Clustering and Structural Balance in Graphs." Human Relations 20
(May) : 181-87.
The Strength of Weak Ties
-.
-. 1969. "Social Structures and Cognitive Structures." In R. P. Abelson et al.,
Theories of Cognitive Consistency. Chicago: Rand McNally.
1970. "Clustering and Hierarchy in Interpersonal Relations." American
Sociological Review 35 (October) : 843-52.
Davis, James A,, P. Holland, and S. Leinhardt. 1971. "Comment." American Sociological
Review 36 (April) : 309-11.
Davis, James A,, and S. Leinhardt. 1971. "The Structure of Positive Interpersonal
Relations in Small Groups." In Sociological Theories in Progress. Vol. 2, edited by
J. Berger, M. Zelditch, and B. Anderson. Boston: Houghton-Mifflin.
Epstein, A. 1969. "The Network and Urban Social Organization." In Social Networks
in Urban Situations, edited by J. C. Mitchell. Manchester: Manchester University
Press.
Frankenberg, R. 1965. Communities in Britain. Baltimore: Penguin.
Gans, Herbert. 1962. The Urban Villagers. New York: Free Press.
Granovetter, M. S. 1970. "Chansng Jobs: Channels of Mobility Information in a
Suburban Community." Doctoral dissertation, Harvard University.
Harary, F. 1965. "Graph Theory and Group Structure." In Readings in Mathematical
Psychology. Vol. 2, edited by R. Luce, R. Bush, and E. Galanter. New York: Wiley.
Harary, F., R. Norman, and D. Cartwright. 1965. Structural Models. New York: Wiley.
Heider, F. 1958. The Psychology of Interpersonal Relations. New York: Wiley.
Holland, Paul, and S. Leinhardt. 1970. "Detecting Structure in Sociometric Data."
American Journal of Sociology 76 (November): 492-513.
-. 1971a. "Transitivity in Structural Models of Small Groups." Comparative
Group Studies 2 :107-24.
-. 1971b. "Masking: The Structural Implications of Measurement Error in
Sociometry." Mimeographed. Pittsburgh: Carnegie-Mellon University.
Homans, George. 1950. The Human Group. New York: Harcourt, Brace & World.
Jacobs, Jane. 1961. The Death and Life of Great American Cities. New York: Random
House.
Kapferer, B. 1969. "Norms and the Manipulation of Relationships in a Work Context."
In Sociel Networks in Urban Situations, edited by J. C. Mitchell. Manchester:
Manchester University Press.
Katz, E., and P. Lazarsfeld. 1955. Personal Influence. New York: Free Press.
Kerckhoff, A., and K. Back. 1968. The June Bug: A Study of Hystevical Contagion.
New York: Appleton-Century-Crofts.
Kerckhoff, A,, K. Back, and N. Miller. 1965. "Sociometric Patterns in Hysterical
Contagion." Sociometry 28 (March): 2-15.
Keyes, L. C. 1969. The Rehabilitation Planning Game. Cambridge, Mass.: M.I.T. Press.
Korte, Charles. 1967. "Small-World Study (Los Angeles) : Data Analysis." Mimeographed.
Poughkeepsie, N.Y.: Vassar College.
Korte, Charles, and Stanley Milgram. 1970. "Acquaintance Networks between Racial
Groups." Journal of Personality and Social Psychology 15 (June) : 101-8.
Laumann, Edward. 1968. "Interlocking and Radial Friendship Networks: A Crosssectional
Analysis." Mimeographed. Ann Arbor: University of Michigan.
Laumann, Edward, and H. Schuman. 1967. "Open and Closed Structures." Paper
prepared for the 1967 ASA meeting. Mimeographed.
Leinhardt, Samuel. 1972. "Developmental Change in the Sentiment Structure of
Childrens' Groups." American Sociological Review 37 (April): 202-12.
Mayer, Adrian. 1966. "The Significance of Quasi-Groups in the Study of Complex
Societies." In The Social Anthropology of Complex Societies, edited by M. Banton.
New York: Praeger.
Mayer, Phillip. 1961. Townsmen or Tribesmen? Capetown: Oxford.
Mazur, B. 1971. "Comment." American Sociological Review 36 (April): 308-9.
Milgram, Stanley. 1967. "The Small-World Problem." Psychology Today 1 (May) :
62-67.
Mitchell, J. Clyde. 1969. Social Networks in Urban Situations. Manchester: Manchester
University Press.
-.
-.
American Journal of Sociology
Newcomb, T. M. 1961. The Acquaintance Process. New York: Holt, Rinehart &
Winston.
Parnes, Herbert. 1954. Research on Labor Mobility. New York: Social Science Research
Council.
Precker, Joseph. 1952. "Similarity of Valuings as a Factor in Selection of Peers and
Near-Authority Figures." Journal of Abnormal and Social Psychology 47, suppl.
(April) : 406-14.
Rapoport, Anatol. 19.53~."Spread of Information through a Population with SocioStructural
Bias. I. Assumption of Transitivity." Bulletin of Mathematical Biophysics
15 (December) : 523-33.
1953b. "Spread of Information through a Population with Socio-Structural
Bias. 11. Various Models with Partial Transitivity." Bulletin of Mathematical
Biophysics 15 (December) : 535-46.
1954. "Spread of Information through a Population with Socio-Structural
Bias. 111. Suggested Experimental Procedures." Bulletin of Mathematical Biophysics
16 (March): 75-81.
-. 1963. "Mathematical Models of Social Interaction." In Handbook of Mathematical
Psychology. Vol. 2, edited by R. Luce, R. Bush, and E. Galanter. New York:
Wiley.
Rapoport, A,, and W. Horvath. 1961. "A Study of a Large Sociogram." Behavioral
Science 6:2 79-9 1.
Rogers, Everett. 1962. Diffusion of Innovations. New York: Free Press.
Shapero, Albert, Richard Howell, and James Tombaugh. 1965. The Structure and
Dynamics of the Defense R G D Indutvy. Menlo Park, Calif.: Stanford Research
Institute.
Simmel, Georg. 1950. The Sociology of Georg Simmel. New York: Free Press.
Solomonoff, Ray, and A. Rapoport. 1951. "Connectivity of Random Nets." Bulletin of
Mathematical Biophysics 13 (June) : 107-17.
Sullivan, Harry Stack. 1953. The Interpersonal Theory of Psychiatry. New York:
Norton.
Tilly, Charles. 1969. "Community:City:Urbanization." Mimeographed. Ann Arbor:
University of Michigan.
Travers, Jeffrey, and S. Milgram. 1969. "An Experimental Study of the 'Small-World'
Problem." Sociometry 32 (December) : 425-43.
Wirth, Louis. 1938. "Urbanism as a Way of Life." American Journal of Sociology 44
(July) : 1-24.