Writing to persuade readers to act is not pure logic. Sometimes this raises suspicions. What are those manipulative writers up to? Why not just make the case and be done without all that emotional rhetoric and red type? (I’m just being hypothetical without implying anything good or bad about red type.)
So here is a true story. I know a man who had a job interview involving a weekend trip to meet his potential supervisor and get acquainted with the workplace. He had a great time and, after he returned, he quickly sent a thank you note to the boss. The boss responded to him that he seemed like a great candidate and had performed well in the interview. Nevertheless, since the candidate had signed the note, he took it upon himself to do some lay handwriting analysis. And he decided on that basis that the candidate was completely unfit for the job.
This is an extreme example, but it is an example of something that happens all the time.
I suppose in some sort of strange society where everyone was trained to only respect strict syllogisms, sales writing might be able to restrict itself to a logical argument with nothing else. But in the actual world, you can’t escape the presence of factors that our outside of logic. The “irrational” is always there to subvert your logic and bypass your arguments.
No writer can afford to ignore this fact–not when he or she is writing for human readers.
Also posted on my business blog.