Sure, a principal that guides conduct, not a principal that controls or dictates conduct. Paladins of Devotion have a rule against lying built into their design. Clerics have the worship of deities built into their class description, and Monks have a rule against being a murder hobo built into their class description. All of these can be ignored, and only the Paladin has further rules expanding upon what happens if they choose to do so. The thing about rules with no mechanical penalties that are ruled only through personal choice is that they stop being true as soon as you make the other choice. Halflings don't suddenly gain a fly speed because they decide they want to fly. If they jump off a building and start flapping their arms, they're only going downward.Especially odd since the definition of a rule includes “a principal that guides conduct”. It’s LITERALLY including a choice as what a rule is defined as, because a person’s principals are choices. I’ve seen people argue some silly things in the past, but I have to admit, I’ve never seen it get this ridiculous. So far, we’ve had him argue that the definition of a rule isn’t a rule, how any DM that uses rules in the rule book (rule is even in that name of what those books are called lol) are tyrants, and another poster say that using that rule to make decisions is an arbitrary decision (the opposite of what arbitrary means).
Is it opposite week and I missed it or something?
But you know what? Go to an AL game with a Druid wearing plate mail and tell the DM you are allowed if you want based on some of the reasons given here. Let me know how that works out for you.
And the arbitrary decision comes from a DM saying the Druid cannot put on the armor. The official rules clarification is that they can choose to do so, because nothing in the game system stops them. The only thing stopping them is if the DM decides it infringes on their story (which is nothing more than a reminder of something inherent to the game as a whole), but in my experience, 90% of campaigns have nothing involving Druidic lore by default. If you say a Druid can't perform an action that the lead designer of the game has said there is nothing in the game system to prevent, and you cannot point at something in the game system that says otherwise, then to say it's impossible is arbitrary. Period.
And it doesn't matter what people at AL say, for reasons I've already explained before. It's also true that there are some AL tables that allow it, and it's legal for them to do so, because it doesn't require a house rule to make it legal as per RAW. The ones that make it illegal as per RAW are simply bias and clinging to the lore of Druids from older editions, especially since their ruling goes against what the lead rules designer says is true. If they tell me SA is official when it comes to iterating the intent of Conjure spells, but then tell me it's not official when clarifying the rules as written in regards to the Druid in metal armor, then I'm assuming arbitrary rulings based on what the DM wants, and not what the book says.
If the developer (via Sage Advice) and publisher (via publishing the Sage Advice as official rules on their site) says something is true, and a DM tells me otherwise, I'm not taking the DM's word for it. The DM has final say in enforcement at their table, but that doesn't mean they're right about what the rules say.