Sword of Spirit
Legend
Iserith, the whole point of choosing an alignment is that you are essentially stating how you are going to roleplay your character! Just as a player who selects the Wizard class is announcing that he intends to play an guy who casts arcane magic spells rather than, say, go about smashing foes with Barbarian rage (unless he multiclasses...), a player who announces that his character is Lawful Good is saying that he is going to play that character a certain way. Selecting the Lawful Good alignment (for instance) excludes the player from declaring that his PC is going to (say) rob the peasants walking down the road, at least if the player is playing his PC according to the alignment he freely selected. If not, he's not roleplaying properly, and should have selected an alignment that allows him to have his character do what he wants. What's the point of having alignments at all, if the allegedly Lawful Good PC can do anything his Chaotic Evil counterpart can do without penalty? If a PC wants to play his character in (say) a Chaotic Evil manner, fine... but he should not be allowed to do so and also claim his character is Lawful Good! You wouldn't allow a character to be defined as a "pirate" and then let the player tell you "Oh, and by the way, he's never been on a boat, knows nothing about seamanship, and is deathly afraid of water", would you?
The only way I think alignment/action correlations should (yes, this is one of the few things in D&D where I think everyone really should do it the way I do it) be handled by the DM is to change the character's alignment if their behavior is clearly out of harmony with it. There is no need to tell the player. They can write whatever they want on the character sheet. "LG", "pirate", "The Great and Almighty Duke of Awesomeland." It doesn't matter at all to the character's actual alignment other than serving as a frame of reference for the DM to interpret from.
If a player calls his character a pirate, but doesn't it back it up at all, the DM can safely ignore it. Just because it is scribbled on a character sheet doesn't make it true. If the character calls himself a pirate, then he is either lying or deluded, and the world will react appropriately (fear, avoidance, or simply ignoring him if they think he's full of it).
Same goes with alignment. If the player thinks his character is LG but acts LE, then in the great library in the DM's head you write "LE" and don't have to tell the player anything. If the character claims he's lawful good (assuming such phrases even exist in the setting), see the pirate example.
It's really easy to do this in 5e, since there are so few ways to find out what a character's actual alignment is, that his real alignment may never come up (unless you have brief scenes in the afterlife when a character dies like I do--and even then it's not necessarily precise) in the entire campaign.
As a DM, I would allow the player at their option to ask me to tell them if they are violating their alignment, and I would make sure anyone who might be bothered to find their character in an undesired afterlife is able to talk with me before the campaign starts so we can get on the same page of interpreting the alignments, but as far as bugging them about it during the campaign? Nah, it's silly.
(If a player was new to D&D alignments, I might give them some cues when they are first getting into the game that they appear to be acting significantly out of harmony with their stated alignment, and that the the general process is that their alignment changes to match their actions, just to make sure they are aware of that and cool with it. I might even ask them if they'd like to change their "declared" alignment.)
