How I know Herman Cain is guilty of sexual harassment

1. He hasn't filed a lawsuit against his accusers
2. He hasn't specifically denied the charges.  Cain has said things like "I haven't harassed anyone".
This is different from:
"I was never in a car with Ms. Bialek"
"I never touched Ms. Bialek".

or even better.
"Ms Bialek is lying."

To the public:
"These are false allegations"  is equal to "Ms. Bialek is a liar".

but legally they aren't.  Cain is using lawyerly words to obfuscate.

If  Cain attacks the accusers character, he would be subject to a libel lawsuit.

BTW. If he does say these and none of the accusers sue, then I would tend to believe Cain unless there was a good reason to wonder why someone would allow another person to blatantly lie about them.