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Persuasion is deeply ingrained in how societies function. Aristotle described three classic rules of verbal or written persuasion. The first is establishing your credibility and authenticity with your audience, possibly by downplaying your own achievements or identifying common ground. This is essential because if the speaker is not perceived as honest, they have already lost their sale. The second is appealing to emotion, a part of human nature that often trumps logic in decision making. The third rule is appealing to reason, that is, make a valid argument.

Although many people have brilliant ideas and honest motives, not everyone is able to win an audience over through persuasion. This has lead many to dub persuasion as an "art," a soft skill that everyone can study, but few can master. However, scientists and marketing professionals are now discovering that when it comes to persuasion, there are scientific variables at play beyond the clever talking and copywriting.

Robert Cialdini, professor emeritus of psychology and marketing at Arizona State University has identified six scientific principles of persuasion:

1. Reciprocity: This is the feeling that you need to return a favor. Ever wonder why a restaurant might hand out free samples or your cable company might throw in HBO for new customers? Once you've had that first taste for free, you're more likely to start paying.
2. Commitment: Hooked on your daily Starbucks? Paid actual money to see all of the "Star Wars" prequels? Tuning in every week, hoping "The Walking Dead" will figure out where it's going? That's commitment. Once you're hooked on a product, it's easier to keep you paying for it. (Even if that payment is just time.) Commitment also accounts for the low-ball approach you hear from car salesmen. Sure, the car's only $10,000. But there's also this cool stereo and a sun roof and an extra cup holder and taxes and fees and now you're staring at $15,000. You don't back away because you already committed at $10,000. Your mind has a hard time pivoting away from the choice you made to buy.
3. Social Proof: We humans have a pack mentality. Researchers report that hotel guests are 29 percent more likely to reuse their towels if they are told most other guests choose to reuse theirs. The percentage jumps to 39 percent if they're told the majority of guests who stayed in that room reused their towels. This is a key tactic of Great Britain's Behavioral Insight Team, also known as the "Nudge Unit." We don't want to be left behind, so we tend to go with the herd.
4. Authority: If Stephen Hawking told you Skittles made you smarter, you might be more likely to head out for a rainbow-colored sugar rush. Hawking is an expert, and we're more likely to be swayed by expertise. Michael Jordan was the perfect pitchman for athletic shoes and sports drinks. Similarly, Sam Waterston is an expert in robot attacks, which made him an excellent spokesman for Old Glory Insurance.
5. Liking: In addition to the opinions of experts, you're more likely to trust the opinions of people similar to you. When that salesperson says you look great in that outfit or compliments your haircut, they're trying to build a rapport. Once you like them, you're willing to trust them.
6. Scarcity: People want what they can't have. That's why we jump to buy limited edition collectibles and overpay for that dream home we just toured. Would the Shamrock Shake or McRib be such a phenomenon if it were available year 'round? Scarcity works via the concept of anticipated regret: we anticipate how bad we'll feel if you miss out on a purchase or experience. Limited time! Act now! Think of all the pumpkin spice flavor you won't be able to savor when spring rolls around!

So the next time you hit the sales floor, keep your ears peeled for these six strategies. Chances are, the sales team will be using at least a few to pry open your wallet.

And if you're on the sales side, consider sharpening your skills with a highly rated how-to guide. Check out "The Science of Selling: Proven Strategies to Make Your Pitch, Influence Decisions, and Close the Deal" by David Hoffeld. The audiobook is free with a trial of Audible.