My eldest asked me at lunch the other day, 'Dad, what is blackmail?'
I gave one answer, my mother-in-law gave a slightly different answer, which led to some investigation and an interesting discovery. From wikipedia:
"Blackmail is the crime of threatening to reveal substantially true information about a person to the public, a family member, or associates unless a demand made upon the victim is met. This information is usually of an embarrassing, socially damaging, and/or criminally incriminating nature. As the information is substantially true, the act of revealing the information may not be criminal in its own right nor amount to a civil law defamation; the crime is making demands in exchange for withholding it. English Law creates a much broader definition of blackmail, covering any unwarranted demands with menaces, whether involving revealing information or not."
Essentially the difference between my mother-in-law and I was that I was using the English Law version, whereas as she was using the stricter (earlier?) definition.
So: in common English terms, blackmail is when someone says 'do this, or you'll be sorry', ie it is the use of force to compel someone to do something that they otherwise would not have done (NB force doesn't have to be physical; I'm using it essentially as a contrast to reason, as in 'reasoning with someone'). It is treating a human being as a thing, an instrument for the will, rather than as a person. In short, it is bullying (in the news at the moment).
I was reminded of this conversation by reading Doug's post. The concept as a whole has been on my mind rather a lot over the last nine months or so.