What is the difference between the Confundus Charm and the Imperius Curse?

Question

Throughout my many readings of the Harry Potter series, I have wondered about the Confundus Charm. There isn't much said about it, but it is used several times throughout the books. My question here is about the usage of the Confundus Charm, and how it differs from the Imperius Curse. To me, it seems as though the Imperius Curse is just a stronger Confundus Charm, and that there is a little bit of overlap between the two spells. I have included several quotes that demonstrate my confusion.

The first, from the final book. Here, Harry uses both the Confundus Charm and the Imperius Curse to obtain the same objective: control other characters that pose a threat.

Knowing that he had only seconds, Harry pointed Draco’s wand at each of the guards in turn and murmured, “Confundo” twice. Unnoticed by Travers, who was looking through the bronze doors at the inner hall, each of the guards gave a little start as the spells hit them . . .
“One moment, madam,” said the guard, raising his Probe.
“But you’ve just done that!” said Hermione in Bellatrix’s commanding, arrogant voice. Travers looked around, eyebrows raised. The guard was confused. He stared down at the thin golden Probe and then at his companion, who said in a slightly dazed voice,
“Yeah, you’ve just checked them, Marius.”

Harry Potter and the Deathly Hallows, p.529

Just later in the chapter, Harry uses the Imperius Curse for a similar effect.

Harry raised the hawthorn wand beneath the cloak, pointed it at the old goblin, and whispered, for the first time in his life, “Imperio!”
A curious sensation shot down Harry’s arm, a feeling of tingling warmth that seemed to flow from his mind, down the sinews and veins connecting him to the wand and the curse it had just cast. The goblin took Bellatrix’s wand, examined it closely, and then said, “Ah, you have had a new wand made, Madam Lestrange!”
“What?” said Hermione. “No, no, that’s mine—”
“A new wand?” said Travers, approaching the counter again; still the goblins all around were watching. “But how could you have done, which wandmaker did you use?”
Harry acted without thinking: Pointing his wand at Travers, he muttered “Imperio!” once more.
“Oh yes, I see,” said Travers, looking down at Bellatrix’s wand, “yes, very handsome. And is it working well? I always think wands require a little breaking in, don’t you?”
Hermione looked utterly bewildered, but to Harry’s enormous relief she accepted the bizarre turn of events without comment.

To me, this seems as though the Imperius Curse, as Alastor Moody says in Harry Potter and the Goblet of Fire, allows the wizard “total control” over the object or person in question (213). But couldn't the Confundus Charm be used to similar effect?

Another difference arises. The Confundus Charm seems to have a different effect on objects. This is seen primarily in Harry Potter and the Goblet of Fire.

After Harry is named as the fourth champion:

“Because they hoodwinked a very powerful magical object!” said Moody. “It would have needed an exceptionally strong Confundus Charm to bamboozle that goblet into forgetting that only three schools compete in the tournament. . . . I’m guessing they submitted Potter’s name under a fourth school, to make sure he was the only one in his category. . . .”

This seems to have "confused" the goblet, as the name of the charm would suggest. However, Moody demonstrates during his class that the Imperius Curse can be used on non-human objects, specifically, a spider. This last quote also shows that the Confundus Charm can be manipulated in different ways, to different extents.

In Harry Potter and the Deathly Hallows, it is implied that Snape used the Confundus Charm rather like one would use the Imperius Curse.

“You will have to give Voldemort the correct date of Harry’s departure from his aunt and uncle’s,” said Dumbledore. Not to do so will raise suspicion, when Voldemort believes you so well informed. However, you must plant the idea of decoys; that, I think, ought to ensure Harry’s safety. Try Confunding Mundungus Fletcher. And Severus, if you are forced to take part in the chase, be sure to act convincingly. . . . I am counting upon you to remain in Lord Voldemort’s good books as long as possible, or Hogwarts will be left to the mercy of the Carrows. . . .” -Dumbledore, Chapter Thirty-Three, p.688

To me, this seems to suggest that the Confundus Charm can be used to great extent, even to the point where one can control another person’s actions, if only on a limited scale.

Another use of the Confundus Charm that seems similar to the Imperius Curse is found at the end of Harry Potter and the Prisoner of Azkaban. Snape implies that Harry, Ron and Hermione were confounded by Sirius Black, but his description of the spell sound more like that of the Imperius Curse.

“Order of Merlin, Second Class, I’d say, First Class if I can wrangle it!”
“Than you very much indeed, Minister.”
“Nasty cut you’ve got there. . . . Black’s work, I suppose?”
“As a matter of fact, it was Potter, Weasley, and Granger, Minister. . . .”
“No!”
“Black had bewitched them, I saw it immediately. A Confundus Charm, to judge by their behavior. They seemed to think there was a possibility he was innocent. They weren’t responsible for their actions. On the other hand, their interference might have permitted Black to escape. . . . They obviously thought they were going to catch Black single-handed…”

Severus Snape and Cornelius Fudge, Chapter Twenty-One, pp.386-387

Then just a little bit later:

“You see, Minister?” said Snape. “Confounded, both of them. . . . Black’s done a very good job on them. . . .”
“WE’RE NOT CONFOUNDED!” Harry roared.

So obviously, the Confundus Charm confuses people or objects, and the Imperius Curse controls people or objects. But my questions remain:

1. Can the Confundus Charm be used to the extent of a weak Imperius Curse, similar to what Snape used on Mundungus?

2. If so, how far can it go?

3. Why isn't the Confundus Charm illegal?

Answer 1

If you're a Star Wars aficionado, think about Confundus as a light Force suggestion (sometimes used by Luke in the EU, at the level - or even less so - of Ben Kenobi's "These are not the droids you are looking for").

While it can theoretically be used to influence other person's actions, it's an indirect influence: you let them believe something they shouldn't (or better yet, simply confuse them into not thinking clearly), but don't force them to choose some action. As such, even Good Guy Jedis sometimes use it.

Imperio is, on the other hand, a direct control of other people's actions and choices, and is very explicitly listed in Star Wars as Dark Jedi/Sith thing to do (Joruus C'Baoth, Emperor Palpatine).

So, the notion of separating minor mental nudge from a bruteforce enforcement of your will seems to be a common enough thing in speculative fiction.

Answer 2

The Confundus Charm is used to confound or confuse. The Imperius Curse is used to control another mind.

The difference is similar to forgetting why you went into a room with a knife versus going into a room and stabbing someone. Under the influence of the Confudus Charm, it could be suggested to you that you were going to stab someone, but if that doesn't make sense at the moment or is something you wouldn't do, you won't do it. However, if you were under the control of the Imperius Curse, you would, as the other wizard was in complete control of your actions.

Confundus causes confusion and can be used to plant ideas in someone's mind. Imperio is used to actually control someone's mind. Confundus can probably go to the point that you believe the story someone tells you, but not to the point that you act against your will. Imperio, cast by a strong wizard upon a weaker one, can go all the way to the point of committing murder, hence the defense by former Death Eaters of being under Imperio explaining their behavior.

As to why the Confundus Charm isn't illegal? Why aren't Memory Charms illegal? Probably because they see widespread use against muggles in maintainence of the International Statute of Wizarding Secrecy.

Answer 3

Like Jesan Fafon said, the Confundus Charm plants ideas in someone's mind, rather than controlling them, like the Imperius Curse. Here's another good example: You wake up in an unfamiliar place, but it's obviously on Earth. Someone tells you that you are in a city, say, Dublin, for example. You would think you were in Dublin because you're confused and your brain wants answers as soon as possible. That is how Snape was able to exert a level of control over Mundungus, by making him think he had the idea (This is also why he paraded the fact that he made the idea, he wanted to be credible for something good).