The person I was contending with is a moral realist, who would say that the function which represents those rules, the rules under which we play chess now, is the correct set of rules, and that this correctness is objective and independent of the minds of chess players.
I explained the point I was making and that wasn't it: The point was what obligation/compulsion means. It doesn't mean it is physically impossible to do what is morally forbidden. It doesn't mean it is an edict you will be punished for disobeying. It does mean that it is logically impossible to be moral (or rational or a chess player) after having significantly departed from the rules.
This person would, I presume, argue that if suddenly every chess player in the world at the same time agreed to eliminate en passant from the game of chess, that they would then be playing the game "wrong".
They would be playing a different game..chess 2.0 or chess++. Plainly, you can't have one player using the revised rules and her opponent the old ones.
to do what is morally forbidden
With your chess analogy, those moves that are forbidden are set by human minds and decisions. The game of chess itself is a product of human intelligence, and they can change the rules over time, and indeed they have.
Are you saying that morality works the same way? That what is morally forbidden are those things which most people find objectionable / assign negative value to?
...They would be playing a different game..chess 2.0 or chess++. Plainly, you can't have one player using the revised rules and her opponent the old on
People who grow up believing certain things,
even if they later stop believing them,
may not quite realize how the beliefs sound to outsiders...
(SCENE: A small cottage in Nazareth.)
Joseph: Mary, my dearest fiancée, there's something I've been meaning to talk to you about.
(Mary's shoulders slump. Slowly, as if under a heavy burden, she turns around to face Joseph.)
Joseph: You seem to be getting fat around the waistline, and throwing up in the morning, and, er, not getting any periods. Which is odd, because it's sort of like -
Mary: Yes! I'm pregnant! All right? I'm PREGNANT!
Joseph: How is that possible?
(Mary's shoulders slump further.) Mary: How do you think?
Joseph: I don't know, that's why I'm asking you. I mean, you're still a virgin, right?
(Mary looks up cautiously, and sees Joseph's face looking blankly puzzled.)
Joseph: Well?
Mary: God did it.
Joseph: You had sex with -
Mary: No! Haha. Of course not. I mean, God just snapped his fingers and did one of those miracle things and made me pregnant.
Joseph: God made you pregnant.
Mary: (Starts to sweat.) Yes.
Joseph: Mary, that is just so... completely...
(Mary's eyes squeeze shut.)
Joseph: ...COOL!
(Mary opens her eyes again, cautiously.)
Mary: You think so?
Joseph: Of course! Who wouldn't think so? Come on, we've got to tell everyone the news!
Mary: Maybe we should keep this between just the two of us -
Joseph: No, no, silly girl, this is way too important! Come on!
(Joseph grabs Mary's wrist and drags her out of the house. SCENE: The gathering square of Nazareth. A dozen well-dressed men, and the town's head rabbi, look on Joseph and Mary impatiently.)
Rabbi: What's this all about, Joseph? I trust there's a good reason for the fuss?
Joseph: Go ahead, Mary! Tell them what you told me.
Mary: Um... (She swallows.) God made me pregnant.
Rabbi, looking stern, yet understanding: Now, Joseph, you know you're not supposed to do that before -
Joseph: No, no, you don't get it! She's still a virgin! God made her pregnant directly!
(There's a long pause.)
Man #1: So, what you're saying here, basically, is that Mary tells you she's a virgin.
Joseph: Uh huh!
Man #2: And you haven't had sex with her.
Joseph: Uh huh!
Man #3: And now she's pregnant.
Joseph: Precisely!
Man #4: So you think that God did it.
Joseph: What other explanation could there be?
Rabbi: Joseph, that is just so... unbelievably...
(Mary holds her breath.)
Rabbi: NEAT!
(Mary exhales.)
Man #5: A miracle! A miracle right here in Nazareth!
Man #6: Wow! I thought that miracles only happened in Jerusalem!
Man #7: Come on! Let's spread the good news!
(They depart. SCENE: Mary is alone with her friend, Betty, in Betty's house.)
Betty: "God did it."
Mary: I panicked! It was all I could think of!
Betty: So who's the real -
(Mary lifts an eyebrow significantly. There's a brief pause.)
Betty: Ah. So that's why the rabbi went along with it.
Mary: Well, he thinks he's the father, anyway. Why, does it matter?
Betty: It puts some things in a different light.
Mary: Like what?
Betty: The rabbi has been telling all the pretty young girls that you, Mary, are the ultimate embodiment of feminine virtue, and when they grow up, they should be just like you -
Mary: I just feel so awful about the whole mess. What kind of thing is this to have hanging over my child's life?
Betty: You've got to put things in perspective, dearie. You told one little white lie. It's not as if you caused the fall of the Roman Empire.
Mary: But what if the Romans hear about it? I don't want my baby to end up being crucified!
Betty: No one's going to obsess about it that long. In a couple of months this whole thing will blow over.
Mary: I hope you're right...
(Exeunt Omnes.)