The Six Principles of Influence (also known as the “Six Weapons of Influence”) were introduced in Cialdini’s book, Influence: The Psychology of Persuasion (1984). A revised edition was published in 2006. Cialdini identified the six principles through experimental studies, and by immersing himself in the world of what he called “compliance professionals” – salespeople, fund raisers, recruiters, advertisers, marketers, and so on. (These are people skilled in the art of convincing and influencing others.)

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Here are the six principles:

1. Reciprocity: As humans, we generally aim to return favors, pay back debts, and treat others as they treat us. According to the idea of reciprocity, this can lead us to feel obliged to offer concessions or discounts to others if they have offered them to us. This is because we’re uncomfortable with feeling indebted to them. For example, if a colleague helps you when you’re busy with a project, you might feel obliged to support her ideas for improving team processes. You might decide to buy more from a supplier if they have offered you an aggressive discount. Or, you might give money to a charity fundraiser who has given you a flower in the street.

2. Commitment (and Consistency): Cialdini says that we have a deep desire to be consistent. For this reason, once we’ve committed to something, we’re then more inclined to go through with it. For instance, you’d probably be more likely to support a colleague’s project proposal if you had shown interest when he first talked to you about his ideas.

3. Social Proof: This principle relies on people’s sense of “safety in numbers.” For example, we’re more likely to work late if others in our team are doing the same, put a tip in a jar if it already contains money, or eat in a restaurant if it’s busy. Here, we’re assuming that if lots of other people are doing something, then it must be OK. We’re particularly susceptible to this principle when we’re feeling uncertain, and we’re even more likely to be influenced if the people we see seem to be similar to us. That’s why commercials often use moms, not celebrities, to advertise household products.

4. Liking: Cialdini says that we’re more likely to be influenced by people we like. Likability comes in many forms – people might be similar or familiar to us, they might give us compliments, or we may just simply trust them. Companies that use sales agents from within the community employ this principle with huge success. People are more likely to buy from people like themselves, from friends, and from people they know and respect.

5. Authority: We feel a sense of duty or obligation to people in positions of authority. This is why advertisers of pharmaceutical products employ doctors to front their campaigns, and why most of us will do most things that our manager requests. Job titles, uniforms, and even accessories like cars or gadgets can lend an air of authority, and can persuade us to accept what these people say.

6. Scarcity: This principle says that things are more attractive when their availability is limited, or when we stand to lose the opportunity to acquire them on favorable terms. For instance, we might buy something immediately if we’re told that it’s the last one, or that a special offer will soon expire.

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Robert Cialdini has spent his entire career researching the science of influence earning him an international reputation as an expert in the fields of persuasion, compliance, and negotiation. His books, including, Influence, are the result of decades of peer-reviewed research on why people comply with requests. Influence has sold over 2 million copies, is a New York Times bestseller and has been published in twenty-seven languages.

Because of the world-wide recognition of Cialdini’s cutting edge scientific research and his ethical business and policy applications, he is frequently regarded as the “Godfather of influence.” Cialdini received his Ph.D from the University of North Carolina and postdoctoral training from Columbia University. He has held Visiting Scholar Appointments at Ohio State University, the University of California, the Annenberg School of Communications, and the Graduate School of Business of Stanford University. Currently, Cialdini is Regents’ Professor Emeritus of Psychology and Marketing at Arizona State University.

Cialdini is President of INFLUENCE AT WORK; focusing on ethical influence training, corporate keynote programs, and the CMCT (Cialdini Method Certified Trainer) program. His clients include such organizations as Google, Microsoft, Cisco Systems, Bayer, Coca Cola, KPMG, AstraZeneca, Ericsson, Kodak, Merrill Lynch, Nationwide Insurance, Pfizer, AAA, Northern Trust, IBM, Prudential, The Mayo Clinic, GlaxoSmithKline, Harvard University – Kennedy School, The Weather Channel, the United States Department of Justice, and NATO.