In response to: Can anybody swear truthfully that they have seen a ghost?
Yes I can.
When I was 18 I was with my girlfriend and several friends at my girlfriend's best friend Mary's house.
Mary's mom wasn't home so we had the house to ourselves.
We were all at the dining room table where someone was rolling a sort of little cigarette (our first of the day so that wasn't really a factor).
Something caught my eye and I turned my head towards the hallway and saw a thin middle-aged man standing there glowering back at me.
I nearly fell out of my chair with surprise.
The others asked me what had surprised me so, and I explained.
Mary asked what the man looked like and I explained: thin, short, swarthy complexion but grey and sickly looking, military haircut, horn-rimmed glasses, wearing pajamas....
Mary said, "oh yeah that's my stepdad's ghost, several people have seen him."
She then went to get a photo of her stepdad and it was the same man I had seen. He had died in that house about 5 years before.
That's my one and only ghost story.