Click on any career advice blog and you’re likely to come upon the popular catchphrase, “It’s not what you know, but who you know.”

Mark Granovetter portrait

Mark Granovetter (Image credit: Do Pham)

The adage emphasizes the importance of social networks in a person’s professional and personal life. While it feels like conventional wisdom now, when the idea first emerged in the scholarly community in a 1973 paper by Stanford sociologist Mark Granovetter, it was considered bold, even groundbreaking.

In a survey he conducted of how 282 men in the United States got their jobs, Granovetter found that a person’s weak ties – their casual connections and loose acquaintances – were more helpful than their strong ones in securing employment.

“Your weak ties connect you to networks that are outside of your own circle,” explained Granovetter in a 2022 interview. “They give you information and ideas that you otherwise would not have gotten.”

Granovetter’s research formed the basis of his doctoral dissertation – he earned his PhD from Harvard in 1970 – and the survey was one among a dozen or so other important studies that he cited in the now seminal paper, “The Strength of Weak Ties.”

Over the past five decades, it has become a classic paper in the social sciences literature, with nearly 70,000 citations from scholars in the fields of business, economics, psychology, and sociology, with far-reaching implications in other disciplines as well.

The strength of the weak tie theory, 50 years on

Weak tie theory has become a foundational concept in sociology, taught in many introductory courses.

Granovetter’s colleague in the sociology department, David Grusky, remembers when he first learned about Granovetter’s weak ties work as an undergraduate at Reed College. At the time, he was thinking through the concept of a butterfly effect, the large effects of random perturbations. “I remember thinking that Mark’s work illuminates why seemingly minor interactions are so powerful within the social world (i.e., they’re packed with information),” Grusky, the Edward Ames Edmonds Professor in the School of Humanities and Sciences and director of the Center on Poverty and Inequality, told Stanford Report. “Although this is a bit of a misreading (I was young!), it’s nonetheless stayed with me and I’ve always thought of Mark as an exemplar when it comes to teasing out sociological mechanisms.”

On the 50-year anniversary of the seminal study’s publication, Grusky interviewed Granovetter about his thoughts on the impact his work has had on students and scholars over the decades.

Granovetter, who has been on the Stanford faculty since 1995 and holds the Joan B. Ford Professorship in the School of Humanities and Sciences, pointed out that more than 90% of citations came after 2000. Over the past 25 years, that period has seen the rise of the internet, which has transformed how people stay connected with one another, especially social media. Online networks created new opportunities for interaction and the exchange of ideas and information, especially among loose acquaintances – an area that makes for an interesting examination of how weak tie theory works.

One Stanford scholar who looked at weak ties in the online world was Erik Brynjolfsson, the Jerry Yang and Akiko Yamazaki Professor and senior fellow at the Stanford Institute for Human-Centered Artificial Intelligence. He, along with MIT’s Sinan Aral, Harvard Business School’s Iavor Bojinov, and others conducted a set of experiments on LinkedIn with 20 million people over five years – the largest empirical examination of weak tie theory in the labor market to date. Their findings, published in Science, revealed Granovetter’s weak tie hypothesis has held up: A person’s weakest ties were the most helpful for career advancement.

The scholars took the theory further: They looked at whether someone’s industry made a difference and found that weak ties were most helpful in more digital sectors of the economy. But in less digital industries, strong ties increased career mobility – a finding that led Brynjolfsson and his co-authors to suggest expanding the theory to include this nuance.

“If I may generalize, a wonderful feature of these papers is that they don’t only try to find out whether I was ‘right’ or not, but they show ways in which the argument needs to be changed, improved, or revised, so that it becomes even stronger (not weaker),” said Granovetter to Grusky about Brynjolfsson’s study, and another recent paper by MIT and University of California, Berkeley, scholar Eaman Jahani. “I do think there’s been real cumulation here.”

Granovetter also credited the many citations of his research to the influence of other notable scholars who have cited his work, particularly Duncan Watts and Steven Strogatz, who helped bring network theory into other fields like physics and computer science. “The moral of the story: If you want 70,000 citations, it’s all about diffusing out of small-pond sociology!” Granovetter said.

Over the decades, Granovetter has expanded upon his weak tie theory to include labor markets more broadly. His 1974 book, republished in 1995, Getting a Job: A Study of Contacts and Careers (University of Chicago Press), Granovetter offered new insights into how networks shape labor market outcomes.

In 2021, there was an article in the journal Social Networks devoted to the theory that demonstrated how it spread across the social sciences. That same year, Granovetter was honored with the BBVA Frontiers of Knowledge Award for his contributions to the field.

But weak tie theory has not been Granovetter’s only contribution to sociology.

“‘The Strength of Weak Ties’ is a foundational paper in social network analysis, and only one of many Mark wrote,” said his Stanford colleague Daniel McFarland. “Every paper he wrote was a gem that still has a lot of sparkle.” In Society and Economy (Harvard University Press, 2017) – Grusky calls it Granovetter’s “magnum opus” – Granovetter “shows that it’s a capital mistake to try to build economic theory that ignores the deep interactions between the economy and the social world in which economies are embedded,” Grusky said. “Although social network processes are one key example of this type of embedding, Mark has gone on to show how economies are also profoundly affected by the religious, scientific, political, and legal contexts in which they are situated.”

Understanding broader implications

As Granovetter pointed out to Grusky, one of the unique aspects to weak tie theory is its iterative qualities and how scholars across fields interpreted it in new and innovative ways. The study has shaped how scholars, including those at Stanford, think about broader implications in society and on problems like inequality.

For example, Stanford economist Matthew Jackson drew upon Granovetter’s theory in his book, The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviors (Vintage, 2020), to explain how a limited network means limited opportunities for economic mobility. As Jackson argued, a person’s network shapes their destiny.

“The concept of weak ties highlights the importance of the reach of people’s networks beyond their family and close friends, and has been one of the most influential ideas in social network analysis,” said Jackson, the William D. Eberle Professor in Economics. “It fundamentally changed people’s understanding of which social relationships are relevant and consequential.”

With the rise of automation, Granovetter sees the importance of weak ties being increasingly relevant.

“No matter what kind of big data or artificial intelligence or machine learning that employers are able to draw on, they will never know as much about a person as someone who actually knows them and has worked with them and knows their personality and knows what they do in their spare time and how they approach problems,” Granovetter explained in a 2022 interview with the BBVA Foundation. “There will always be more knowledge to be gotten from personal contacts of individuals than you can get from any kind of informatics.”

Grusky, Brynjolfsson, and Jackson are also senior fellows at the Stanford Institute for Economic Policy Research.