One of the earliest studies on how micro-level interaction affects the macro-level structure of a social network was done by Granovetter (1973). He argued that the processes within interpersonal networks translate small-scale interactions into large-scale patterns. He analysed various macro-level phenomena, such as diffusion, social mobility, political organisation and social cohesion, as investigated by different researchers and discussed their results. He emphasised weak ties, and argued that they play a greater role in social phenomena like innovation and diffusion than strong ties.
Many interpersonal ties indeed form large social networks. On the most macro level, if two persons form a strong tie between them, then it is more likely that if a third person forms a tie with either of the two, he will also form a tie with the other one. Further, as time passes, these bonds are likely to become stronger and to form a close triad (Heider, 2013, Newcomb, 1961). Thus people with similar personalities bond together over time, and the strongly-connected triads merge to form a larger group. However, for a social network, this strongly-connected group cannot scale up infinitely, because persons cannot maintain strong ties with an infinite number of people, and also they have certain differences of choice. In this way, a large social network is likely to be formed by different strongly-knitted smaller groups. Now, the groups might not be fully isolated; persons from different groups can also form ties with each other. Granovetter (1973) argued that these inter-group bonds are more likely to be weak ties; this is because, if a strong tie is formed between groups, then the other friends in the groups are also likely to befriend each other, and the partition will eventually collapse. This suggests that if one person wants to communicate with others from the different group, it should be through one of the weak ties. Thus the persons connected by the weak tie act as a local bridge.
Now if a rumour or novel information is to be diffused in the network, then it is through the weak ties by which it spreads further. Using a similar explanation, Granovetter (1973) argued that marginal figures are ‘early adopters’, able to spread the innovation successfully because they might be rich in weak ties. He further explained his weak tie
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argument using the results of two experiments. The first one was the ‘small world’ experiment done by Milgram and his associates. In the experiment, Milgram gave packets or booklets to random persons in several United States cities. The task for them was to send the booklet to the person’s address as given in the packet. And, because they did not know the recipients, they needed to send them to some of their friends whom they think could know the recipient or can forward to other correspondences to keep the process running. The experiment was done in several modified way but the overall principal was the same – to send a booklet to unknown recipient through correspondence and check how many hops it takes to reach. Granovetter pointed out that when the first transfer of the booklet is from a White to a Negro ‘acquaintance’ (considered a weak tie), then the success rate of reaching the destination is 50% (Korte, 1967, Korte and Milgram, 1970). In contrast, that rate falls to 26% when the first transfer is from a White to a Negro ‘friend’ (considered a strong tie). This can indicate that weaker interracial ties are more effective in bridging social distance. The second experiment Granovetter used to explain his results was by Rapoport and Horvath (1961). Some (N = 851) students were asked to write to eight of their best friends in order. Networks were traced by considering two consecutive choices of best friends. It was observed that the most students were found in a network when only the last two choices were considered, and the least were found when the first two choices were considered. Granovetter argued that this indicates that strong ties result in overlapped networks.
Finally, Granovetter (1973) elaborated on the implications of his weak tie argument and the findings of the above described experiments on both micro and macro levels of a social network, citing some empirical results to illustrate these implications. On the micro level, Granovetter’s theory implies that the fewer indirect contacts one has, the more encapsulated he will be in terms of knowledge of the world beyond his own friendship circle. Granovetter developed this point empirically by citing some results from a labour market study where he investigated how workers find new jobs through personal contacts as opposed to any other methods. He found that, in most cases, the workers (55.6%) found their jobs through contacts whom they saw occasionally. Also, the path length of
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the information flow (i.e., number of intermediaries) in most cases (45.3%) was 1, thus strengthening his weak tie claim.
On the macro level, Granovetter (1973) discussed why some communities organise for common goals effectively, whereas others seem unable to adapt to doing so. As an example, he cited the Italian community of Boston’s West End, who were unable to fight against urban renewal and were ultimately destroyed. He argued that the West End community might have been partitioned into isolated cliques, resulting in a lack of significant communication paths due to the absence of weak ties between the groups. Thus trust relationships between leaders and citizens were hampered, rendering unsuccessful the campaign against the urban renewal.