GigaKnight, what are your thoughts on Soul's Attendant vs Soul Warden? This seems like such a perfect example.
I think the problem you describe is much more prevalent in Magic than in Dominion, simply because in Magic you have a lot more cards out on the field usually, and a lot more triggered effects that could happen. Just this week, someone in my playgroup had a Soul's Attendant out, and didn't gain life when an opponent played a creature (5-player game). By the time it was realized, it was too late, and he couldn't get the life. Had it been a Soul Warden instead, he would have.
Although, this issue arises because of the casual and fast nature of the way people play. The fact is, his Soul's Attendant DID trigger, and it's ability DID go on the stack. That still happens ever though it's "may." Once the ability resolves, at that point he can choose to do it or not. But because we were playing fast and loose, no one ever stopped to say "ok, a creature was just played, now what does the stack look like?" In the same way, in a casual setting, players may play a card or ability, and then another card or ability, without stopping and "passing priority" to the other players.
I guess what I'm saying is in that example, I feel like in a way the group made an illegal play just like we would have if it had been a Soul Warden instead. Because we never actually put the triggered ability on the stack. The guy didn't wait until it resolved and then chose not to gain life. Rather, it never went on the stack, and never resolved, because he forgot to put it on the stack.
Yeah, those cards are a good example; I would go with may.
You raise a very interesting point about the stack in Magic, though. So you're saying you think you'd be required to put
the decision itself on the stack with Soul's Attendant? I'm very curious to know what a rules judge would say here. I've never heard of a
decision going on the stack, but I haven't played since well before they removed "damage on the stack".
But the fact that they removed "damage on the stack" makes it clear to me that
not everything goes on the stack. Is there a clear ruling about what does / doesn't go on the stack? As I think about this more, I'd be surprised if decisions go on the stack. It seems like the stack is place for
game events, not meta-events like decisions. So this is what I'd expect: the creature coming into play goes on the stack. When it resolves, if the player opts to gain a life, the life gain goes on the stack. But I could be wrong.
I don't think the issue would really apply to Dominion since it doesn't have an explicit stack. I think of "you may" as "when X happens, you are allowed to do Y". Just as, when I stand up right now, I'm allowed to walk to the bathroom. I'm also allowed to walk outside. If I don't even think about any of these things, I just don't do them.
Player B observes player A's mistake. Player B now has an opportunity to call out Player A on his mistake. By not doing so, he is cheating (according to Gigaknight's idea of cheating).
This is certainly unethical, but I don't think the communities for most board/card games would label it outright cheating. Just speculating, though. I imagine that in some games, it's hard to draw a line with that kind of ethical obligation, anyway (between reminding a player of their legal options, and actually giving them strategic advice).
There's an interesting discussion on something similar to this over at bgg: http://boardgamegeek.com/thread/15032/quotforgettingquot-the-colonist-ship.
The BGG thread mentions that Puerto Rico has an explicit rule about what happens when a specific required step is forgotten. That's a very interesting idea to me. Donald could also add a ruling about that to Dominion, I suppose. My guess is that it would be functionally equivalent to "you may" in most cases; the thing just doesn't happen. That would make intentionally "forgetting" a legal loophole instead of rules violation: ethically dubious but not forbidden. I'm not sure if I like that or not.
Actually, Donald, if you're still reading this, can you make a ruling about that? E.g. what if somebody plays a Haggler, buys a card, and forgets to gain another one? What if the mistake is caught early enough to reset game state? What if it's caught too late for that?
And would that ruling apply to all triggered abilities?
EDIT: Clarifications