http://wiki.dominionstrategy.com/index.php/Way_of_the_Butterfly
Instructions say: "You may return this to its pile to gain a card costing exactly $1 more than it."
So it's already optional to use the Way. Seems odd to me so I suspect I am missing something.
Other than allowing you to get another card in play that you wouldn't want to play normally (for example for Conspirator), why would you ever opt into Way of the Butterfly and then not have it doing anything?
The effects of the action card still apply so are there cards where its effect is good but not its play steps?
Way of the Rat is also optional.
Butterfly needs an "if you do/to" to stop Throne Room tricks. And Donald X. isn't a fan of "do this. If you do..."
In my experience, "You may pay $4. If you do..." is simpler than "Pay $4. If you do..." It makes the "if you do" make more sense; there's no, wait why does that say "if" when I'm forced to?
And for Way of the Rat, it wants the gaining to require a treasure discard. "Discard a Treasure. Gain a copy of this" doesn't work without an "or reveal you can't," so adding "you may" is the other option.
I'm not sure if this has been asked before, or maybe someone just understands it. Why do Advance, Quest, Delay and Enhance start with "you may"? Does it make any difference, since you could just choose not a buy it?
You could just choose not to buy it, but Donald X. doesn't like creating cards where accountability could be an issue. If Advance said, "trash an Action card from your hand," then there is no way for other players to know if you have an Action card in your hand. This never matters, because why would you choose to buy Advance otherwise, but maybe in the future there will be a Reaction discard-attack type thing which reacts to buying an Event, or something.
Correct. For those four in particular, you may not be able to do the thing, and it's telling you to do the thing; "you may" is the tersest way to deal with "keeping you honest." In practice it doesn't matter - since you'd just not buy the Event - but it's a good habit picked up from it actually mattering for kingdom cards.
In some cases, "you may" helps me get a more natural phrasing; I prefer not to tell you to do something and then check if you did it, because it looks weird to casual players.
For online play, the "you may" can be annoying; you wouldn't have clicked on whatever if you didn't want to do it, and sure don't need to be asked again. That's the kind of thing that can be fixed with an autoplay though.
Now obviously you can find tons of inconsistencies in how cards are worded (for example, Madman and Turtle don't have "you may", and Courtier and Scrap have way different wordings). And well that's not really a thing that has an explanation.
We may have talked about it but there's no real reason there. The cards try to be phrased well and are not all phrased at once.
I don't know if there was a reason. It got this wording and this wording seemed fine; the usual story when people want the story of the wording.