There is a really neat study on how emotional and logical priming affects consumer choice described in the book Made to Stick. In 2004 Carnegie Mellon did a study to determine whether people are more motivated to give to a cause if they were primed emotionally rather than logically.
Subjects took an irrelevant survey in which they were paid 5 one dollar bills. They were unexpectedly given an opportunity to donate a portion of their payment to charity.
The first group was given a request letter that gave statistical evidence about the masses of needy people, for example: “In Zambia severe rainfall deficits have resulted in a 42% drop in maize production from 2000, as a result an estimated 3 million Zambians face hunger”.
The second group was given a request letter that told an emotional story about a single girl.
“Any money you donate will go to Roqea, a seven year old from Maui Africa. Roqea is desperately poor and faces the threat of severe hunger and even starvation. Her life will be changed for the better as a result of your financial gift.”
The logically primed people gave an average of $1.14 while the emotionally primed gave $2.38.
Then the researchers tried to give a third group both sets of information, thinking a emotional argument paired with a logical argument would encourage people to give more. This group gave an average of 1.43.
The study not only showed emotional priming was more than twice as effective as logical, it showed that logical thinking can interfere with emotional thinking. The researchers suggested that when people think analytically, it makes it difficult for them to think emotionally.
If your goal is to persuade, focus on the emotional and avoid logic.