Strength of Weak Ties

Journal Article: http://www.stanford.edu/dept/soc/people/mgranovetter/documents/granstrengthweakties.pdf
Summary of the theory: http://www.analytictech.com/networks/weakties.htm

Mark Granovetter, a sociologist now at Stanford, is considered to be one of the most frequently referenced of all organizational scholars. In 1973, he wrote "The Strength of Weak Ties" (SWT), "a seminal article that’s been cited a jaw-dropping 5111 times according to Google Scholar."

The first link is the actual article published in the American Journal of Sociology. Granovetter was motivated by wondering why it is that people so often get jobs from weak ties, and how large groups coordinate to make things happen! He talks about how weak ties and strong ties work...

People with many weak ties [Toennies’ Gesellschaft] live up to the expectations of several others in different places and at different times, which makes it possible to preserve an inner core — to withhold inner attitudes while conforming to various expectations. People with strong ties [Gemeinschaft] share norms so thoroughly that little effort is needed to gauge intentions of others.

He also talks about how strong ties are responsible for and make difficult, the adoption of innovation.

More weak ties, more capable of acting in concert. Strong ties breed local cohesion and macro fragmentation.

For a more concise explanation, the second link contains a summary of what Granovetter says in his article. The diagram is quite clear and is worth taking a look at!