Soul Mutilation
Harry Potter and the Half-Blood PrinceVoldemort's creation of Horcruxes demonstrates how Dark Magic can corrupt and destroy the soul, making him less human.
increasing
Bearing strength in each event
decreasing
The Horcrux Theory

The Dark Art
The Explanation
Albus Dumbledore explains that a Horcrux is an object containing a piece of a wizard's soul, created by committing murder. Voldemort has made multiple Horcruxes, splitting his soul into seven parts.
The Corruption
Creating Horcruxes deforms the soul and makes the wizard less human. Voldemort's appearance becomes snake-like, and his emotions are stunted.
The Danger
The Horcruxes are the key to Voldemort's immortality. They must be destroyed before he can be killed. This is Harry's mission.
The Destruction of the Ring

The Cost of Horcrux Hunting
The Attempt
Dumbledore finds and destroys Marvolo Gaunt's ring, a Horcrux. However, the ring's curse damages his hand and hastens his death.
The Price
Destroying a Horcrux is dangerous. Dumbledore's sacrifice shows the high cost of fighting Dark Magic.
The Lesson
Harry learns that the path to defeating Voldemort is fraught with danger. He must be prepared to pay a price.
late December, after learning the memory
referenced throughout, but Dumbledore's hand shows the cost