The Science of Persuasion: The Argument
A strong argument contains points that are logically sound, easily defendable and compelling. It is tailored to your audience’s level of motivation and knowledge on the topic and often provides them with persuasive evidence — such as statistics, relevant facts, etc. Before and during the presentation, the audience should be instructed and given time to carefully think about the message.
Another component of a strong argument is to primarily elicit favorable thoughts in the audience, especially when you are arguing against their initial position. All good car salespeople know that to get you to buy a more expensive car, they should start with the extra luxury, status and experience the vehicle can bring you.
A weak argument, on the other hand, not only lacks supporting evidence and has weak logic, but it also tends to evoke unfavorable attitudes in the audience. Therefore, if you want to convince someone who is against vaccination that vaccination is important, don’t start with attacking their character (e.g., you are an awful human being).
However, a strong argument cannot always win you the business or the support you need. Here are some elements you can apply when presenting your argument.
As strong arguments are packed with logic, reasoning and information, they naturally require the audience to use more cognitive resources to process them. All those details can be a lot to absorb. Therefore, a lot of distractions can result in your argument becoming less effective. It is especially disruptive for motived audiences because it hinders their ability to receive and process the messages.
But distraction seems to lead to a preferable outcome for weak arguments, so adding a moderate number of distractions during the presentation of weak arguments can lead to an increase in the effectiveness of the argument. Some explain this interesting result as a function of the audience justifying the efforts they put into these distractions (I spent so much time and effort listening to these messages, it must be good.),2 while some find it is because the audience’s negative attitudes toward the weak arguments were actually distracted (This presentation is bad…Oh, wait! A funny joke!...A cute puppy picture!...This presentation is not that bad!).
Length of information
Researchers found that the attitudes of a low-knowledge audience can be affected by length of the presentation (the longer, the better). But the same is not true for audiences who are highly knowledgeable on the topic. Highly knowledgeable audiences only care about the strength of the argument, not the length.
The number of arguments contained in a persuasive message is also an important factor in the audience’s attitudes. For a not-so-motived audience (read my first blog of the series on knowing your audience), the more arguments presented, the more favorable attitudes they will have toward the information, strong and weak arguments alike. For audiences who are motivated to process the message, the more strong arguments you present, the more favorable attitudes they will have for the message. However, for these audiences, the more weak arguments you give, the less likely they will endorse your information.
It has been found in many studies that repeating a persuasive message will first increase and then decrease agreement, due to excessive exposures. However, as strong arguments contain a lot of information and require a lot of the audience’s attention and energy to process, repeating the information can help the audience better understand the message, which in turn leads to greater agreement with it. On the other hand, repeating a weak argument can progressively weaken the listeners’ attitudes toward it.
How many times should you repeat a message? It depends on the length of the information. The lengthier the information is, the more repetitions may be necessary.1 If you really are not sure how many times you should repeat your message, three times should be your primary choice.
The science of persuasion is not only fascinating, but it is also closely related to our daily lives. If you are interested in the topic and want to learn more, check out the works by Professor Richard E. Petty from The Ohio State University.
I hope this series is helpful to your incoming persuasion attempts. On my next blog, we will start a new topic: how to build trust.
 Petty, R.E. & Cacioppo, J.T. (1986). The elaboration likelihood model of persuasion. Advances in Experimental Social Psychology, 19, 123-206.
 Baron, R. S., Baron, P., & Miller, N. (1973). The relation between distraction and persuasion.
Psychological Bulletin, 80, 310-323.
 Petty, R. E., & Brock, T. C. (1981). Thought disruption and persuasion: Assessing the validity of
attitude change experiments. In R. Petty, T. Ostrom, & T. Brock (Eds.), Cognitive responses in
persuasion (pp. 55-79). Hillsdale, NJ: Erlbaum.
 Petty, R.E., Wells, G.L., & Brock, T.C. (1976). Distraction can enhance or reduce yielding to propaganda: Thought disruption versus effort justification. Journal of Personality and Social Psychology, 34, 874-884.
 Petty, R.E., & Cacioppo, J.T. (1984). The effects of involvement on responses to argument quantity and quality: Central and peripheral routes to persuasion. Journal of Personality and Social Psychology, 46, 69-81.
 Cacioppo, J. T., & Petty, R. E. (1979). Effects of message repetition and position on cognitive
responses, recall, and persuasion. Journal of Personality and Social Psychology, 37, 97- 109.
 Cacioppo, J. T., & Petty, R. E. (1980a). Persuasiveness of communications is affected by exposure
frequency and message quality: A theoretical and empirical analysis of persisting attitude change.
In J. H. Leigh & C. R. Martin (Eds.), Current issues and research in advertising. Ann Arbor:
University of Michigan Graduate School of Business Administration.
 Cacioppo, J.T., & Petty, R.E. (1989). Effects of message repetition on argument processing, recall, and persuasion. Basic and Applied Social Psychology, 10, 3-12.
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