For more than 35 years, psychology professor Robert Cialdini has been studying the science of persuasion to figure out what makes people say "yes."

One of the tricks Cialdini discovered is as simple as doing this one thing: ask for advice.

But the key, says Cialdini, is that you must use the word "advice."

"Let's say you have an idea and you would like to get buy in from colleagues so you can move it up the line and get it adopted by your superiors," Cialdini, 76, tells CNBC Make It.

Typically, people would ask for their colleagues' opinions. But that's a mistake, according to his research.

"When you ask for someone's opinion, you get a critic," Cialdini says.

The word "opinion," triggers the other person to step back from you psychologically and become critical of your idea, says Cialdini.

But "it turns out if you change one word, and instead of asking for that person's 'opinion,' you ask for that person's 'advice,' they take a step towards you," he says.

The word "advice" triggers the person to see themselves as a partner in forging the idea.

And a partner is more useful than a critic: According to Cialdini, research shows that using the word "advice" over "opinion" gets you "significantly more favorable reactions to the same idea."

"There's a quote attributed to [novelist Saul Bellow] that says, 'When we ask for advice, we're usually looking for an accomplice,'" Cialdini says.

Science backs that up that, according to Cialdini. "If you get that advice, you get that accomplice," he says.

Cialdini outlines many other persuasion tricks he's researched in his newly revised 1984 New York Times best-selling book "Influence: The Psychology of Persuasion."

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