By Dr. Ken Broda-Bahm:
The belief is that “fast-talking” applies easily to “lawyer,” just as it naturally attaches to “salesman,” "politician," or other perceived “slicks” who are able to persuade before their targets quite realize what is happening. But does speed of speech really convey an advantage in persuasion? The answer is a solid, “It depends.” The research cuts both ways. It turns out that faster or slower speaking doesn’t just influence comprehension or credibility, but cognition as well: The factor that makes faster speech more effective in some contexts, but not in others, has to do with what is going on in the minds of those on the receiving end of the message.
It is a practical point for litigators, and one of many questions they need to ask as they adapt to the jury, the bench, the arbitrator, the mediator, the client, or the other side. When do you ramp things up and when do you ease off? The somewhat nuanced advice from the research is that it depends on whether your target audience at that moment is more likely to lean in your favor, or to lean against you on the specific point you are making. When that audience is predisposed against you, then a faster rate is more effective because it tends to limit the amount of internal counterargument the audience is able to engage in. But when the audience is likely to be in your corner already, then a slower rate will free that audience up to reinforce your message as you present it. This dynamic is one more example of a fundamental principle of persuasion: Audiences are active, not passive. Instead of just thinking about what works on them, it helps to also think about what they’ll do with your appeal.