Guilt

During the opening of the play, Macbeth makes it clear that he doesn't want to kill Duncan. He calls the idea a "horrid image" and says that it will "shake his single state of man" so violently that he won't be able to do it. He argues that he should be "shutting the door" against anyone who wants to kill Duncan, and that Duncan's death will be so awful that even the Angels will rage "trumpet tongued" against his death. So Macbeth seems to know that killing Duncan won't get what he wants, but he does it anyway. As a result, quite predictably, he feels really guilty afterwards.

Here are some key quotes looking at Macbeth's regret for what he did to Duncan:

I had most need of blessing, and 'Amen' stuck in my throat - Just after killing Duncan, Macbeth must have said a prayer but he cannot say Amen which suggests that God cannot bless him.

Methought I heard a voice cry 'Sleep no more! Macbeth does murder sleep', the innocent sleep. - The fact that Macbeth stops being able to sleep is commonly cites as being a result of him feeling guilty. However, although there are repeated connections between sleep and innocence the line "sleep no more! Macbeth does murder sleep" is written in speech marks, and Macbeth clearly says that he "heard a voice cry" it, and it's what the witches did to the sailor during the opening, so it would seem to make much more sense that Macbeth can't sleep as a result of the witches' magic spell than any sense of guilt.

I am afraid to think what I have done; - Macbeth doesn't fear the Norwegian army, but he is afraid to face what he's done.

Will all great Neptune's ocean wash this blood / Clean from my hand? - The image of having blood on your hands runs through Macbeth, and here he's arguing that even all the water in the sea won't wash his hands clean of their guilt.

We sleep / In the affliction of these terrible dreams / That shake us nightly: - Regardless of who caused his inability to sleep, Macbeth cannot sleep throughout most of the play. Here, he talks about his sleep being haunted by terrible dreams that shake him awake again. This is a clear reference to how he cannot escape his guilt for what he's done.

better be with the dead ... Than on the torture of the mind to lie / In restless ecstasy. - In this quote he can't sleep, but lies with his mind being tortured. In fact, it is so bad that he would rather be dead!

O, full of scorpions is my mind, dear wife! - This is the classic line to show Macbeth's unstable mental state. Scorpions attack from both ends, they're desert dwellers - like the serpent from the Bible - and they're inside his brain; the centre of his sense of self.

However, despite this Macbeth quickly finds himself in a position where he can't go back. He says that he is "in blood stepp'd so far that should I wade no more, Returning were as tedious as go o'er." Which is essentially a way of saying that he's already done so much wrong that it would be as bad to go back as to continue. And so, although he feels guilty, he doesn't turn back and eventually kills Banquo as well as Macduff's wife and child, and seems pretty non-plussed about his wife's death when that gets announced. As a result of all this, it's tough to feel that sorry for him.

Below, I've gathered a collection of quotes from the play that reflect the mess that Macbeth is in by the end. He feels bad about killing more people, but can't seem to stop himself:

I am in blood / Stepp'd in so far that, should I wade no more, / Returning were as tedious as go o'er: - This is a great line when looking at Macbeth's mental state. Here, he claims that he's so knee deep in blood that it's as "tedious" to continue killing people as it would be to try to return to his old state of decency. "Tedious" is a pretty crazy word to use to describe what he's talking about, but the image is clear: he's over committed now, so he may as well see the whole thing through...

I have almost forgot the taste of fears; - Remember when Macbeth was afraid to think on what he'd done? Well by the end that is not the case... he's committed so many terrible acts that he's forgot what it feels like to be afraid of anything! His life is a big old mess and that's pretty much how he ends up...

When it comes to guilt, Lady Macbeth comes up most often. She starts the play being adamant that she will feel no regret - she's the classic image of the psychopathic killer. She remains like this for Acts 1, 2 and 3 (though there are four lines in Act 3 where she's a bit sorry.) She doesn't appear in Act 4 at all, then, suddenly in Act 5 she's so full of regret that she commits suicide.

So, in a nutshell, her character arc goes:

Act 1: No remorse
Act 2: No remorse
Act 3: No remorse
Act 4: No appearance
Act 5: suicidal regret

On the back of this, it's not unreasonable to argue that her character arc is a little lacking. When did she change her mind? Did something happen to change it? What motivated her to rethink her actions? Why did she just suddenly realise what she'd done, and go through one of the biggest u-turns in literary history, entirely off-stage? Shakespeare never really explains, and it's absolutely reasonable to argue that this constitutes a considerable missing element in the play.

Stop up the access and passage to remorse - in Lady Macbeth's magic spell from act 1 scene 5 she asks the spirits to stop her from feeling any "remorse" - which means regret or guilt. So here, she is using magic to stop guilty feels from being able to access her.

The bit when she said she'd kill her own baby - if ever there was a sign that someone lacked the capacity to feel regret or remorse it's the fact that they say they'd kill their own baby to fulfil a promise. Lady Macbeth really is psychotically ruthless.

These deeds must not be thought / After these ways; so, it will make us mad - one thing with this play is that the characters quite often predict what will eventually happen to them. Here, Lady Macbeth recognises that if they spend too long thinking about what they've done - if they dwell on their feelings of guilt - that it will make them mad. Which is exactly what happens to her!

My hands are of your colour; but I shame / To wear a heart so white. - Here, Lady Macbeth claims that her hands are as bloody as Macbeth's but she'd be ashamed to pretend that she was pure. She accepts what she's done and won't pretend to feel guilty when she doesn't. She won't pretend to have a pure white heart when she knows her heart is bad.

Things without all remedy / Should be without regard: what's done is done. - here, she's basically saying that if you can't do anything to fix something, you shouldn't think about it. She's arguing that because they can't change what they've done they shouldn't worry about it anymore. There is no time or space in Lady Macbeth's world for feelings of guilt.

NOTE: there are LOADS more of these, but they're a pretty good selection

Nought's had, all's spent,
Where our desire is got without content:
'Tis safer to be that which we destroy
Than by destruction dwell in doubtful joy.

These four lines from Act 3 are really important as they're the only time prior to her sleepwalking scene that she expresses anything close to any regret for what they've done. Really, to take her character from not feeling any guilt to feeling so much that she's suicidal takes a change in her character which we don't ever see.

But really, if you look closer at these lines she's not actually feeling regret for what they've done, she's just angry that they've got what she wanted but still aren't happy. She's also troubled by the fact that they're not safe in their position, which isn't really a feeling of regret at all but just a concern for their position.

So really, she doesn't actually express any regret until she suddenly becomes suicidal.

Out, damned spot! out, I say! - here, Lady Macbeth is sleepwalking and trying to wash the blood from her hands. The most common argument here is that she cannot escape what she's done - she has blood on her hands and she cannot escape that fact. She discovers, in fact, that you can boss other people around, but she cannot manage her own conscience. This is what eventually brings her down.

What, will these hands ne'er be clean? ... Here's the smell of the blood still: all the / perfumes of Arabia will not sweeten this little hand. - these two lines come from the same scene where she's fretting about the blood on her hands.

It is very telling though that Lady Macbeth's expressions of guilt come while she's sleepwalking. Sleeping - and dreaming - are often considered to be interesting states as they allow us to get in touch with our subconscious. Here, it could be that Shakespeare is saying that although Lady Macbeth may seem like she feels no guilt, she is actually just repressing it. It's possible that Shakespeare is really just saying that even someone as evil as Lady Macbeth can't escape her subconscious feelings of guilt.

This is a completely reasonable question and if you're going to mention this idea in an essay you should really look at this. Without being able to ask Shakespeare himself, I've put together a few ideas that seem reasonable:

a) If we'd spent time with her, going through the slowly dawning process of remorse, there was a danger that we'd develop some sympathy for her position. Shakespeare didn't want this. Because the whole point of the play was to put people off doing what she did, any element of sympathy for her would have been frowned upon by King James. As a result, Shakespeare cut out her descent into madness, and made sure we feel no sympathy for her at all.

b) She was a woman and, as such, her character didn't need to be as developed as the male characters on stage. The play itself is really a study in Macbeth's motivations anyway, and although his wife steals the scenes she's in she's only ever a secondary character. You could argue that there was just no need to delve into her reasons that deeply.

c) She never actually felt any regret consciously... this is a tough one to argue but the fact is that the only time we see her feeling regret is when she's sleepwalking; so she really only dreams the regret that we see. Here, Shakespeare could be highlighting the way that you can't escape your actions, even if it only in your sleep that they come back to haunt you. This argument is complicated a little when you consider that she killed herself, but....

The fact is that we think Lady Macbeth killed herself because Malcolm says that Macbeth's "fiend-like queen, Who, as 'tis thought, by self and violent hands Took off her life." But this is the only reference to her having killed herself.

During the action of the play, we hear some women screaming off stage and then a character called Seyton (whose name sounds suspiciously like Satan) goes to check on her and comes back saying she's dead. Now, I'm not saying that Satan killed her and then Malcolm just cast it aside on the grounds that she was dead and he didn't need to know anymore, but it actually makes a lot more sense of her character arc if she was killed by Seyton and his minions rather than that she killed herself.

Whichever way you choose to look at it, the fact remains that Shakespeare doesn't spend long enough on her regret for me to find her character arc very believable, and although you should avoid directly criticising Shakespeare you're well within your rights to observe this.