There is no single key to a successful persuasive speech. Some people take longer than others to be persuaded, and some respond to different persuasion techniques. Therefore, persuasive speakers should be cognizant of audience characteristics to customize the pitch.
The psychology of persuasion is best exemplified by two theories that try to explain how people are influenced.
Robert Cialdini, in his book on persuasion, defined six "weapons of influence:"
- Reciprocity: People tend to return a favor. In Cialdini's conferences, he often uses the example of Ethiopia providing thousands of dollars in humanitarian aid to Mexico just after the 1985 earthquake, despite Ethiopia suffering from a crippling famine and civil war at the time. Ethiopia had been reciprocating for the diplomatic support Mexico provided when Italy invaded Ethiopia in 1937.
- Commitment and Consistency: Once people commit to what they think is right, they are more likely to honor that commitment even if the original motivation is subsequently removed. For example, in car sales, suddenly raising the price at the last moment works because buyers have already decided to buy.
- Social Proof: People will do things they see other people are doing. In one experiment, if one or more person looked up into the sky, bystanders would then look up to see what they could see. This experiment was aborted, as so many people looked up that they stopped traffic.
- Authority: People will tend to obey authority figures, even if they are asked to perform objectionable acts. Cialdini cites incidents like the Milgram experiments in the early 1960s and the My Lai massacre in 1968.
- Liking: People are easily persuaded by other people whom they like. Cialdini cites the marketing of Tupperware, wherein people were more likely to buy from others they liked. Some of the biases favoring more attractive people are discussed, but generally more aesthetically pleasing people tend to use this influence over others.
- Scarcity: Perceived scarcity will generate demand. For example, saying that offers are available for a "limited time only" encourages sales.
The second theory is called Relationship Based Persuasion. It was developed by Richard Shell and Mario Moussa. The overall theory is that persuasion is the art of winning over others. Their four step approach is:
- Survey your situation: This step includes an analysis of the persuader's situation, goals and challenges.
- Confront the five barriers: Five obstacles pose the greatest risks to a successful influence encounter - relationships, credibility, communication mismatches, belief systems, and interest and needs.
- Make your pitch: People need a solid reason to justify a decision, yet at the same time many decisions are made on basis of intuition. This step also deals with presentation skills.
- Secure your commitments: In order to safeguard the longtime success of a persuasive decision, it is vital to deal with politics at both the individual and organizational level.