Determining informed consent

Here's an interesting wrinkle for you. What about when informed consent is impossible?

For example impact play. I can explain what will happened, precisely what I intend to do, the physics behind the impact, likely physiological and psychological consequences, but that really doesn't matter. Someone who has never been hit before will have no reference for any of that. It will be nothing but their belief they are prepared to experience it, not reality and hardly informed.

This discussion just reminded me of a partner I had long ago that I completely forgot about, but it might be helpful to some who have worry issues about informed consent with regard to impact play (which is a main component in my brand of foreplay).
Somehow, I ran across this cute, short girl who wanted to play. I told her she probably wouldn't like my style. She asked what I meant by that. I told her I am a sadistic dominant and began explaining it to her. Although I tried to make it sound brutal, she still asked me for my address. A few days later, she came over to my house and I immediately marched her in to sit down at the computer where I called up a half-dozen S & M videos I had stored in my video file folder and played the weakest one first finally graduating to an absolute merciless breast flogging of a girl tied to a St Andrews cross, performed by Master Rick Savage. She watched all the videos and wanted to try it. I told her that I would begin with light stuff like in the first video and graduate slowly to the more brutal stuff like in the last video. I gave her a safe word in case her bondage was too tight or if the intensity was too much for her. I told her that she could decline to try any of the harder core stuff and that the intensity would be gradual until I found her limits and that I would go slow at first, but could gradually speed up the strikes, but she could slow it down by saying the word "mercy" if she didn't like it. She was receptive.
I took her into the dungeon and placed a spreader bar between her ankles and tied her wrists to a ceiling hook and stretched her tight in a standing spread-eagle position fully nude. I picked up floggers beginning with the softest one and ending with meanest one. At some point I told her to stick her chest out and suck her belly in. She complied with enthusiasm and stayed that way till I was finished. She was totally into it, and never uttered the safe word even when I was using the last whip.
She came over several times after that, until about two months later, I saw her with her arm all swollen and asked what happened to her. She claimed that she tried to inject herself with heroine using a dirty needle and got badly infected, but the doctors cleaned out her arm and saved her. I never saw her again after that.
Anyway, the videos gave her a visual of how the girls reacted to the impacts and my explanation of what would happen during the session may have given her some re-assurance. She took everything with glee and enthusiasm. She may have been a little kinky before I met her but afterward she was a total masochist. Too bad she disappeared.

Subtle-You seem to have missed my point entirely. How can someone to consent to something they have no frame of reference for? I used impact play as an example as it is simplest to demonstrate. How do you know what it is to be hit (no matter with what or how hard) if you have never been hit? This of course is just a kinky adaptation of the ethical dilemma of any layperson being asked to judge specific technical matter beyond their competence.

Betty-Theory is black and white, life is gray. Which makes it so much harder to deal with. As for this I suppose we would have to parse the difference between between knowledge and wisdom...which I think is the idiom. Knowing and understanding. I can tell you hour by hour what happened at the Battle of Gettysburg, who fought where, how many died, what weapons were used. That in no way means I know what it is like to have experienced the battle.

Something I didn’t see mentioned is that partners should talk to each other about how to handle if the sub goes into subspace.
Personally, there have been times where I’m not completely aware and everything feels good in the moment. So it’s possible that I might not safeword something that I would have if I was completely in my right mind. This is why it’s key for a Dom to know his sub and to be able to recognize for them both when things might be going too far. I’m lucky to have a Dom that I can trust to do that for me.

Yes ma'am. Whichnie another reason I don't understand how people go and meet someone and then play with them. Maybe I'm a prude. Idk.

I don’t think that makes you a prude. That makes you careful and there’s nothing wrong with that!