like can a LG person commit murder or a CE do something kind and expect nothing in return? does lt depend on the dm? 

Alignment is the result of your actions, not the cause.

I'd recommend thinking of alignment as a description of your character, rather than a cause.

Make your character concept. Figure out what drives them, what they would and wouldn't do. Then describe that in terms of alignment (and other in-game features like bonds and flaws) to remind yourself and other players of it.

You can certainly come up with a "Lawful Good" character that would commit murder in some circumstances, or a "Chaotic Evil" one that can do generous and kind things.

Also, a lot of tables ignore alignment.  For the ones that don't, you don't have to do anything you don't want to.  Good people do bad things, bad people do good things.  Characters are no different.  

You come across a Hag disguised as an old woman. You know she is shady but your investigation roll fails. A LG won't attack until he is absolutely sure that she is a hag, while a CN or any E would just stab her to find out. 

Alighnment is a guideline for you how to act, and you can change it if it doesn't fit your character. 

Oh, and LG don't murder people. They execute villains for the greater good. 

Also, remember that your alignment isn't set in stone. Your character's experiences in the game can change how they act, and they would be considered to have a different alignment.

For example, one of the players in my current campaign started out as Lawful Good. But over time she started to notice corruption in the government, and also her strict adherence to her code of honor actually ended up getting people hurt because she couldn't bring herself to do what it takes to protect them. She gradually shifted until she's now somewhere between Neutral Good and Chaotic Good.

In previous editions of D&D there were a lot more restrictions based on alignment (some spells or classes could only be used by specific alignments), but that's gradually been lessened and now alignment is more of a guide to help players roleplay rather than a restriction that controls your actions.

Mirroring what's (mostly) been said: Actions determine alignment, not the other way around.  You should never think "I am (alignment), therefore (action)," it's "I perform (actions), therefore I am (alignment)."

Secondary details: A single action, no matter how heinous, doesn't cause an alignment shift.  It requires consistent behavior; if a LG person flips their crap and murders someone to death for no reason, that's not going to cause a shift (especially not a full shift to CE like a lot of DMs would do).  They'd have to do so repeatedly over a significant length of time.

And I definitely support the idea of forgetting alignment completely and just coming up with your character's personality, motivations, etc and play that.  Nobody fits neatly into one of nine boxes describing them.  The concepts of good and evil are pretty much unquantifiable anyway; philosophers have debated on their definitions for millennia and not come to a consensus, so it's highly unlikely a bunch of gamer geeks are going to be able to do so.  Alignment is really pretty stupid and was obsolete the day it was created.

thanks everyone for the feedback.

I would have said alignment is a guide. It is how you should act. If you are lawful good, but are always a murder hobo, then you are not acting how your character has said they would like to be. It is true, all people real and imagined make mistakes. But if you are a holy man that isn't holy, your DM should start penalizing your character in the form of your deity not helping when you attempt to cast a spell (cleric) or perhaps your deity will mandate some sort of character cleansing.

Part of the role-play is finding out about your character and trying to make the decisions that this fictional person would make. Your choices should have consequences. Unlike some of the other comments here, I really like alignment. I think it helps outline who you are, and how would react. A lawful good character would help the damsel in distress. A chaotic neutral character may, because they are interested in why they are distressed. A chaotic evil character may want to see if they can help with the mayhem. It should not dictate all your choices, but should absolutely help guide you.

You have it backwards, BrassZeus.  Your actions determine your alignment, not the other way around.

The use of Alignment in the game has diminished over various editions. It used to be that there were alignment restrictions for certain classes. Paladins at one point could only be Lawful Good, Druids had to be True Neutral, and I think there were rules about what alignments the worshippers/Clerics of each deity could have. In 5E, alignment has very few mechanical effects, and is much more of a descriptive feature for your character. It's up to your group to decide how to enforce the relationship between a character's declared alignment and their actual behavior. 

Quote from DnDNewper >>

like can a LG person commit murder or a CE do something kind and expect nothing in return? does lt depend on the dm? 

Quote from BrassZeus >>

I would have said alignment is a guide. It is how you should act. If you are lawful good, but are always a murder hobo, then you are not acting how your character has said they would like to be. It is true, all people real and imagined make mistakes. But if you are a holy man that isn't holy, your DM should start penalizing your character in the form of your deity not helping when you attempt to cast a spell (cleric) or perhaps your deity will mandate some sort of character cleansing.

Part of the role-play is finding out about your character and trying to make the decisions that this fictional person would make. Your choices should have consequences. Unlike some of the other comments here, I really like alignment. I think it helps outline who you are, and how would react. A lawful good character would help the damsel in distress. A chaotic neutral character may, because they are interested in why they are distressed. A chaotic evil character may want to see if they can help with the mayhem. It should not dictate all your choices, but should absolutely help guide you.

Quote from FoxfireInferno >>

You have it backwards, BrassZeus.  Your actions determine your alignment, not the other way around.

Neither of these is completely correct.  Alignment is sort of like the Druid's restriction on metal armor.  Wearing metal armor doesn't remove your Druid class, nor suppress your druidic powers.  Being a Druid doesn't prevent you from donning metal armor.  Being a Druid involves not wanting, nor being willing to, don metal armor.

Similarly, being a certain alignment doesn't prevent you from doing anything at all.  Nor does doing anything in particular mean you should be penalized in any way because of its non-adherence to your chosen alignment.  Picking an alignment, as a player, means you're deciding your character will act in a certain way.

Alignment choice is a player decision, which serves as a rough guideline of how that player is pre-deciding how their character would behave.  If a player decides their character is Lawful Good, the player is saying "my character will behave in an orderly manner, respecting rules and laws, and will seek to benefit and help others".  A Lawful Good character is certainly free to murder anyone they come across, for whatever reason, but their character has stated that their character will not, in fact, kill anyone without reason and right.  If a Lawful Good character's player starts deciding to have their player murder wantonly, they're (the player, that is) not honoring the decision they made on character creation.  Whether the DM should punish the character, or the player, for not honoring that decision should be left up to the DM and player.

The reason why many people say "actions dictate alignment" is because in-game, that's how it works.  People who behave like the "Lawful Good" alignment dictates are Lawful Good.  But the players are not "in-game", and the characters are created before they get to act, so saying "actions dictate alignment" isn't appropriate when talking about players and the decisions they make for their characters.  A more appropriate statement could be "acting in discordance with your chosen alignment results in alignment change": if you choose an alignment for your character, but after creation act otherwise, your character's alignment should change to one concordant with your actions.

This is why many people decide to play without a "hard coded" alignment.  You can certainly choose to play your character in accordance to the "Lawful Good" alignment without writing down "Lawful Good" on your character sheet.  That character will be, in fact, Lawful Good.  But if you're unsure how you want to play your character, or you want to change how you play them, having "Lawful Good" on your character sheet can be a problem.

The response to the question, "can a LG person commit murder or a CE do something kind and expect nothing in return?", is a hard "yes".  They certainly can.  In doing so, though, they're acting differently to what their players decided when the characters were created, so a more important question would be "would a LG character's player choose to have their character commit murder, or a CE character's player choose to have their character do something kind and expect nothing in return?".  I'd answer that with a question (asked of the player): "Why?".  There can be several answers to that question, with different implications.  "Because the circumstances make this act more important than the character's values/personality" (e.g. the LG paladin realizes that only by murdering this innocent person will they be able to save the kingdom) could have the character suffering internal conflict for a while, as they ponder the inappropriateness of their actions, and in some cases even some external complications, like the paladin's deity questioning their actions, and maybe even suppressing their powers until they atone.  "Because that's really how they'd behave" could involve an alignment change ("in-game", the character's alignment wouldn't change, it would've been the new one all along, it was just chosen incorrectly by their player), or it could mean the alignment system can't fully codify the character's actual alignment (say, a LG fighter, who behaves in accordance to the LG alignment all the time, except when their family is threatened, in which case they'll stop at nothing to protect them, including flat-out murdering innocents out of a paranoid belief they're plotting to harm the family).

In short, unless it actually matters (like, say, for determining whether a particular Wizard can attune to a particular Robe of the Archmagi), don't worry too much about it, but talk to your players to make sure why they picked the alignments they picked for their characters.

Quote from Lunali >>

Alignment is the result of your actions, not the cause.

 QFT.

Alignment is a one- or two-word description of your character's actions. If your character is untrustworthy, unpredictable, and inconsistent most of the time then we can simply use the label "chaotic". If your character shows no concern about the welfare of others, always treating people as things, then we can use the label, "evil".

What you write on your character sheet does not determine your character's alighnment. So, why did you write it down? Usually one of two reasons. Either you wrote down what your character aspires to be, or you wrote it down as a reminder to yourself, "This character is neutral evil.

Its a  guideline.  A way to summarize your prior actions succinctly on how you generally act by default.  Its not perfect and could/should be overridden by flaws, bonds and ideals as well as circumstance.

And it could change of course.  It should if the choices reflect a different ethos.  It can be a useful guideline if you want to use that way.  Its not a strightjacket...unless you want it to be one to reflect an inner struggle.

But otherwise, mechanically it has lost much of its meaning.  Even on death, I think judgement or the character is based on the sum of their actions, before being sent to the Outer plane as a petitioner, not what you wrote.  Maybe you want to be LG but couldn't live up to it.   I would note that and move on.

From Wiki

"Richard Bartle's Designing Virtual Worlds noted that alignment is a way to categorize players' characters, along with gender, race, character class, and sometimes nationality. Alignment was designed to help define role-playing, a character's alignment being seen as their outlook on life. A player decides how a character should behave in assigning an alignment, and should then play the character in accordance with that alignment.
A character's alignment can change. If a lawful neutral character consistently performs good acts, when neutral or evil actions were possible, the character's alignment will shift to lawful good. In games, the Dungeon Master (referee) decides when alignment violations occur, as it is subjective and often frowned upon, if not outright disallowed."

These are some good points, and I think states what everyone has been saying. I like that the rules state that alignment is all about attitude. Your character may not always do the right thing, but if you are lawful good, you will have the attitude to try. Your attitude is that you want to see society succeed and be a functioning member of that. Not that you won't get mad at some jerk who spits in your drink.

I knew DMs who considered Alignment only in situations directly affected by Alignment, such as detection or interacting with deities and the like. Two DMs I knew decided how the characters were being played and decided the alignments based on the characters' actions when it came time for Alignment-based consequences. If a player contested the decision, the player had to explain how the character's actions fit within the alignment that the player wanted the character to be. This would only happen if a player's character IC knew about the required Alignment. Otherwise, it was all behind-the-screen effects without explanation of how Alignments affected the outcome.

Quote from EricHVela >>

I knew DMs who considered Alignment only in situations directly affected by Alignment, such as detection or interacting with deities and the like. Two DMs I knew decided how the characters were being played and decided the alignments based on the characters' actions when it came time for Alignment-based consequences. If a player contested the decision, the player had to explain how the character's actions fit within the alignment that the player wanted the character to be. This would only happen if a player's character IC knew about the required Alignment. Otherwise, it was all behind-the-screen effects without explanation of how Alignments affected the outcome.

That's kinda awesome.  I'm totally stealing this!